v5: Forms update (#28450)

* Initial spike of consolidated form checks

* Stub out forms rearrangement

- Prepping to drop non-custom file and range inputs
- Prepping to merge custom and native checks and radios (with switches)
- Prepping to merge custom select with form select
- Moving docs arround so forms has it's own area given volume of CSS

* Move input group Sass file to forms subdir

* Start to split and move the docs around

* Simpler imports

* Copyediting

* delete overview file

* Remove commented out code

* remove the custom-forms import

* rewrite flex-check as form-check, replace all custom properties

* Remove old forms doc

* stub out new subpage link section

* update migration guide

* Update nav, forms overview in page nav, and descriptions

* fix check bg position

* fix margin-top calculation

* rename .custom-select to .form-select

* Update validation styles for new checks

* add some vertical margin, fix inline checks

* fix docs examples

* better way to do this contents stuff, redo the toc while i'm at it

* page restyle for docs while here

* un-callout that, edit text

* redo padding on toc

* fix toc

* start to cleanup checks docs

* Rewrite Markdown tables into HTML

* Redesign tables, redo their docs

* Replace Open Iconic icons with custom Bootstrap icons

* Redesign the docs navbar, add a subheader, redo the sidebar

* Redesign docs homepage a bit

* Simplify table style overrides for docs tables

* Simplify docs typography for page titles and reading line length

* Stub out icons page

* Part of sidebar update, remove migration from nav.yml

* Move toc CSS to separate partial

* Change appearance of overview page

* fix sidebar arrow direction

* Add footer to docs layout

* Update descriptions

* Drop the .form-group class for margin utilities

* Remove lingering form-group-margin-bottom var

* improve footer spacing

* add headings to range page

* uncomment form range css

* Rename .custom-range to .form-range

* Drop unused docs var

* Uncomment the comment

* Remove unused variable

* Fix radio image sizing

* Reboot update: reset horizontal ul and ol padding

* de-dupe IDs

* tweak toc styles

* nvm, fix dropdown versions stuff

* remove sidebar nav toggle for now

* broken html

* fix more broken html, move css

* scss linting

* comment out broken helper docs

* scope styles

* scope styles

* Fixes #25540 and fixes #26407 for v5 only

* Update sidebar once more

* Match new sidenav order

* fix syntax error

* Rename custom-file to form-file, update paths, update migration docs for previous changes in #28696

* rename back

* fix size and alignment

* rename that back too

16 files changed, 846 insertions, 1037 deletions

diff --git a/scss/_custom-forms.scss b/scss/_custom-forms.scss
deleted file mode 100644
index ce49f3060a..0000000000
--- a/scss/_custom-forms.scss
+++ /dev/null
@@ -1,514 +0,0 @@
-// Embedded icons from Open Iconic.
-// Released under MIT and copyright 2014 Waybury.
-// https://useiconic.com/open
-
-
-// Checkboxes and radios
-//
-// Base class takes care of all the key behavioral aspects.
-
-.custom-control {
-  position: relative;
-  display: block;
-  min-height: $font-size-base * $line-height-base;
-  padding-left: $custom-control-gutter + $custom-control-indicator-size;
-}
-
-.custom-control-inline {
-  display: inline-flex;
-  margin-right: $custom-control-spacer-x;
-}
-
-.custom-control-input {
-  position: absolute;
-  z-index: -1; // Put the input behind the label so it doesn't overlay text
-  opacity: 0;
-
-  &:checked ~ .custom-control-label::before {
-    color: $custom-control-indicator-checked-color;
-    border-color: $custom-control-indicator-checked-border-color;
-    @include gradient-bg($custom-control-indicator-checked-bg);
-    @include box-shadow($custom-control-indicator-checked-box-shadow);
-  }
-
-  &:focus ~ .custom-control-label::before {
-    // the mixin is not used here to make sure there is feedback
-    @if $enable-shadows {
-      box-shadow: $input-box-shadow, $input-focus-box-shadow;
-    } @else {
-      box-shadow: $custom-control-indicator-focus-box-shadow;
-    }
-  }
-
-  &:focus:not(:checked) ~ .custom-control-label::before {
-    border-color: $custom-control-indicator-focus-border-color;
-  }
-
-  &:not(:disabled):active ~ .custom-control-label::before {
-    color: $custom-control-indicator-active-color;
-    background-color: $custom-control-indicator-active-bg;
-    border-color: $custom-control-indicator-active-border-color;
-    @include box-shadow($custom-control-indicator-active-box-shadow);
-  }
-
-  // Use disabled attribute instead of :disabled pseudo-class
-  // Workaround for: https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/11295231
-  &[disabled] {
-    ~ .custom-control-label {
-      color: $custom-control-label-disabled-color;
-
-      &::before {
-        background-color: $custom-control-indicator-disabled-bg;
-      }
-    }
-  }
-}
-
-// Custom control indicators
-//
-// Build the custom controls out of pseudo-elements.
-
-.custom-control-label {
-  position: relative;
-  margin-bottom: 0;
-  color: $custom-control-label-color;
-  vertical-align: top;
-
-  // Background-color and (when enabled) gradient
-  &::before {
-    position: absolute;
-    top: ($font-size-base * $line-height-base - $custom-control-indicator-size) / 2;
-    left: -($custom-control-gutter + $custom-control-indicator-size);
-    display: block;
-    width: $custom-control-indicator-size;
-    height: $custom-control-indicator-size;
-    pointer-events: none;
-    content: "";
-    background-color: $custom-control-indicator-bg;
-    border: $custom-control-indicator-border-color solid $custom-control-indicator-border-width;
-    @include box-shadow($custom-control-indicator-box-shadow);
-  }
-
-  // Foreground (icon)
-  &::after {
-    position: absolute;
-    top: ($font-size-base * $line-height-base - $custom-control-indicator-size) / 2;
-    left: -($custom-control-gutter + $custom-control-indicator-size);
-    display: block;
-    width: $custom-control-indicator-size;
-    height: $custom-control-indicator-size;
-    content: "";
-    background: no-repeat 50% / #{$custom-control-indicator-bg-size};
-  }
-}
-
-
-// Checkboxes
-//
-// Tweak just a few things for checkboxes.
-
-.custom-checkbox {
-  .custom-control-label::before {
-    @include border-radius($custom-checkbox-indicator-border-radius);
-  }
-
-  .custom-control-input:checked ~ .custom-control-label {
-    &::after {
-      background-image: $custom-checkbox-indicator-icon-checked;
-    }
-  }
-
-  .custom-control-input:indeterminate ~ .custom-control-label {
-    &::before {
-      border-color: $custom-checkbox-indicator-indeterminate-border-color;
-      @include gradient-bg($custom-checkbox-indicator-indeterminate-bg);
-      @include box-shadow($custom-checkbox-indicator-indeterminate-box-shadow);
-    }
-    &::after {
-      background-image: $custom-checkbox-indicator-icon-indeterminate;
-    }
-  }
-
-  .custom-control-input:disabled {
-    &:checked ~ .custom-control-label::before {
-      background-color: $custom-control-indicator-checked-disabled-bg;
-    }
-    &:indeterminate ~ .custom-control-label::before {
-      background-color: $custom-control-indicator-checked-disabled-bg;
-    }
-  }
-}
-
-// Radios
-//
-// Tweak just a few things for radios.
-
-.custom-radio {
-  .custom-control-label::before {
-    // stylelint-disable-next-line property-blacklist
-    border-radius: $custom-radio-indicator-border-radius;
-  }
-
-  .custom-control-input:checked ~ .custom-control-label {
-    &::after {
-      background-image: $custom-radio-indicator-icon-checked;
-    }
-  }
-
-  .custom-control-input:disabled {
-    &:checked ~ .custom-control-label::before {
-      background-color: $custom-control-indicator-checked-disabled-bg;
-    }
-  }
-}
-
-
-// switches
-//
-// Tweak a few things for switches
-
-.custom-switch {
-  padding-left: $custom-switch-width + $custom-control-gutter;
-
-  .custom-control-label {
-    &::before {
-      left: -($custom-switch-width + $custom-control-gutter);
-      width: $custom-switch-width;
-      pointer-events: all;
-      // stylelint-disable-next-line property-blacklist
-      border-radius: $custom-switch-indicator-border-radius;
-    }
-
-    &::after {
-      top: calc(#{(($font-size-base * $line-height-base - $custom-control-indicator-size) / 2)} + #{$custom-control-indicator-border-width * 2});
-      left: calc(#{-($custom-switch-width + $custom-control-gutter)} + #{$custom-control-indicator-border-width * 2});
-      width: $custom-switch-indicator-size;
-      height: $custom-switch-indicator-size;
-      background-color: $custom-control-indicator-border-color;
-      // stylelint-disable-next-line property-blacklist
-      border-radius: $custom-switch-indicator-border-radius;
-      @include transition(transform .15s ease-in-out, $custom-forms-transition);
-    }
-  }
-
-  .custom-control-input:checked ~ .custom-control-label {
-    &::after {
-      background-color: $custom-control-indicator-bg;
-      transform: translateX($custom-switch-width - $custom-control-indicator-size);
-    }
-  }
-
-  .custom-control-input:disabled {
-    &:checked ~ .custom-control-label::before {
-      background-color: $custom-control-indicator-checked-disabled-bg;
-    }
-  }
-}
-
-
-// Select
-//
-// Replaces the browser default select with a custom one, mostly pulled from
-// https://primer.github.io/.
-//
-
-.custom-select {
-  display: inline-block;
-  width: 100%;
-  height: $custom-select-height;
-  padding: $custom-select-padding-y ($custom-select-padding-x + $custom-select-indicator-padding) $custom-select-padding-y $custom-select-padding-x;
-  font-family: $custom-select-font-family;
-  @include font-size($custom-select-font-size);
-  font-weight: $custom-select-font-weight;
-  line-height: $custom-select-line-height;
-  color: $custom-select-color;
-  vertical-align: middle;
-  background: $custom-select-background;
-  background-color: $custom-select-bg;
-  border: $custom-select-border-width solid $custom-select-border-color;
-  @include border-radius($custom-select-border-radius, 0);
-  @include box-shadow($custom-select-box-shadow);
-  appearance: none;
-
-  &:focus {
-    border-color: $custom-select-focus-border-color;
-    outline: 0;
-    @if $enable-shadows {
-      box-shadow: $custom-select-box-shadow, $custom-select-focus-box-shadow;
-    } @else {
-      box-shadow: $custom-select-focus-box-shadow;
-    }
-
-    &::-ms-value {
-      // For visual consistency with other platforms/browsers,
-      // suppress the default white text on blue background highlight given to
-      // the selected option text when the (still closed) <select> receives focus
-      // in IE and (under certain conditions) Edge.
-      // See https://github.com/twbs/bootstrap/issues/19398.
-      color: $input-color;
-      background-color: $input-bg;
-    }
-  }
-
-  &[multiple],
-  &[size]:not([size="1"]) {
-    height: auto;
-    padding-right: $custom-select-padding-x;
-    background-image: none;
-  }
-
-  &:disabled {
-    color: $custom-select-disabled-color;
-    background-color: $custom-select-disabled-bg;
-  }
-
-  // Hides the default caret in IE11
-  &::-ms-expand {
-    display: none;
-  }
-}
-
-.custom-select-sm {
-  height: $custom-select-height-sm;
-  padding-top: $custom-select-padding-y-sm;
-  padding-bottom: $custom-select-padding-y-sm;
-  padding-left: $custom-select-padding-x-sm;
-  @include font-size($custom-select-font-size-sm);
-}
-
-.custom-select-lg {
-  height: $custom-select-height-lg;
-  padding-top: $custom-select-padding-y-lg;
-  padding-bottom: $custom-select-padding-y-lg;
-  padding-left: $custom-select-padding-x-lg;
-  @include font-size($custom-select-font-size-lg);
-}
-
-
-// File
-//
-// Custom file input.
-
-.custom-file {
-  position: relative;
-  display: inline-block;
-  width: 100%;
-  height: $custom-file-height;
-  margin-bottom: 0;
-}
-
-.custom-file-input {
-  position: relative;
-  z-index: 2;
-  width: 100%;
-  height: $custom-file-height;
-  margin: 0;
-  opacity: 0;
-
-  &:focus ~ .custom-file-label {
-    border-color: $custom-file-focus-border-color;
-    box-shadow: $custom-file-focus-box-shadow;
-  }
-
-  // Use disabled attribute instead of :disabled pseudo-class
-  // Workaround for: https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/11295231
-  &[disabled] ~ .custom-file-label {
-    background-color: $custom-file-disabled-bg;
-  }
-}
-
-.custom-file-label {
-  position: absolute;
-  top: 0;
-  right: 0;
-  left: 0;
-  z-index: 1;
-  display: flex;
-  height: $custom-file-height;
-  border-color: $custom-file-border-color;
-  @include border-radius($custom-file-border-radius);
-  @include box-shadow($custom-file-box-shadow);
-}
-
-.custom-file-text {
-  display: block;
-  flex-grow: 1;
-  padding: $custom-file-padding-y $custom-file-padding-x;
-  overflow: hidden;
-  font-family: $custom-file-font-family;
-  font-weight: $custom-file-font-weight;
-  line-height: $custom-file-line-height;
-  color: $custom-file-color;
-  text-overflow: ellipsis;
-  white-space: nowrap;
-  background-color: $custom-file-bg;
-  border-color: inherit;
-  border-style: solid;
-  border-width: $custom-file-border-width;
-  @include border-left-radius(inherit);
-}
-
-.custom-file-button {
-  display: block;
-  flex-shrink: 0;
-  padding: $custom-file-padding-y $custom-file-padding-x;
-  margin-left: -$custom-file-border-width;
-  line-height: $custom-file-line-height;
-  color: $custom-file-button-color;
-  @include gradient-bg($custom-file-button-bg);
-  border-color: inherit;
-  border-style: solid;
-  border-width: $custom-file-border-width;
-  @include border-right-radius(inherit);
-}
-
-// Range
-//
-// Style range inputs the same across browsers. Vendor-specific rules for pseudo
-// elements cannot be mixed. As such, there are no shared styles for focus or
-// active states on prefixed selectors.
-
-.custom-range {
-  width: 100%;
-  height: calc(#{$custom-range-thumb-height} + #{$custom-range-thumb-focus-box-shadow-width * 2});
-  padding: 0; // Need to reset padding
-  background-color: transparent;
-  appearance: none;
-
-  &:focus {
-    outline: none;
-
-    // Pseudo-elements must be split across multiple rulesets to have an effect.
-    // No box-shadow() mixin for focus accessibility.
-    &::-webkit-slider-thumb { box-shadow: $custom-range-thumb-focus-box-shadow; }
-    &::-moz-range-thumb     { box-shadow: $custom-range-thumb-focus-box-shadow; }
-    &::-ms-thumb            { box-shadow: $custom-range-thumb-focus-box-shadow; }
-  }
-
-  &::-moz-focus-outer {
-    border: 0;
-  }
-
-  &::-webkit-slider-thumb {
-    width: $custom-range-thumb-width;
-    height: $custom-range-thumb-height;
-    margin-top: ($custom-range-track-height - $custom-range-thumb-height) / 2; // Webkit specific
-    @include gradient-bg($custom-range-thumb-bg);
-    border: $custom-range-thumb-border;
-    @include border-radius($custom-range-thumb-border-radius);
-    @include box-shadow($custom-range-thumb-box-shadow);
-    @include transition($custom-forms-transition);
-    appearance: none;
-
-    &:active {
-      @include gradient-bg($custom-range-thumb-active-bg);
-    }
-  }
-
-  &::-webkit-slider-runnable-track {
-    width: $custom-range-track-width;
-    height: $custom-range-track-height;
-    color: transparent; // Why?
-    cursor: $custom-range-track-cursor;
-    background-color: $custom-range-track-bg;
-    border-color: transparent;
-    @include border-radius($custom-range-track-border-radius);
-    @include box-shadow($custom-range-track-box-shadow);
-  }
-
-  &::-moz-range-thumb {
-    width: $custom-range-thumb-width;
-    height: $custom-range-thumb-height;
-    @include gradient-bg($custom-range-thumb-bg);
-    border: $custom-range-thumb-border;
-    @include border-radius($custom-range-thumb-border-radius);
-    @include box-shadow($custom-range-thumb-box-shadow);
-    @include transition($custom-forms-transition);
-    appearance: none;
-
-    &:active {
-      @include gradient-bg($custom-range-thumb-active-bg);
-    }
-  }
-
-  &::-moz-range-track {
-    width: $custom-range-track-width;
-    height: $custom-range-track-height;
-    color: transparent;
-    cursor: $custom-range-track-cursor;
-    background-color: $custom-range-track-bg;
-    border-color: transparent; // Firefox specific?
-    @include border-radius($custom-range-track-border-radius);
-    @include box-shadow($custom-range-track-box-shadow);
-  }
-
-  &::-ms-thumb {
-    width: $custom-range-thumb-width;
-    height: $custom-range-thumb-height;
-    margin-top: 0; // Edge specific
-    margin-right: $custom-range-thumb-focus-box-shadow-width; // Workaround that overflowed box-shadow is hidden.
-    margin-left: $custom-range-thumb-focus-box-shadow-width;  // Workaround that overflowed box-shadow is hidden.
-    @include gradient-bg($custom-range-thumb-bg);
-    border: $custom-range-thumb-border;
-    @include border-radius($custom-range-thumb-border-radius);
-    @include box-shadow($custom-range-thumb-box-shadow);
-    @include transition($custom-forms-transition);
-    appearance: none;
-
-    &:active {
-      @include gradient-bg($custom-range-thumb-active-bg);
-    }
-  }
-
-  &::-ms-track {
-    width: $custom-range-track-width;
-    height: $custom-range-track-height;
-    color: transparent;
-    cursor: $custom-range-track-cursor;
-    background-color: transparent;
-    border-color: transparent;
-    border-width: $custom-range-thumb-height / 2;
-    @include box-shadow($custom-range-track-box-shadow);
-  }
-
-  &::-ms-fill-lower {
-    background-color: $custom-range-track-bg;
-    @include border-radius($custom-range-track-border-radius);
-  }
-
-  &::-ms-fill-upper {
-    margin-right: 15px; // arbitrary?
-    background-color: $custom-range-track-bg;
-    @include border-radius($custom-range-track-border-radius);
-  }
-
-  &:disabled {
-    &::-webkit-slider-thumb {
-      background-color: $custom-range-thumb-disabled-bg;
-    }
-
-    &::-webkit-slider-runnable-track {
-      cursor: default;
-    }
-
-    &::-moz-range-thumb {
-      background-color: $custom-range-thumb-disabled-bg;
-    }
-
-    &::-moz-range-track {
-      cursor: default;
-    }
-
-    &::-ms-thumb {
-      background-color: $custom-range-thumb-disabled-bg;
-    }
-  }
-}
-
-.custom-control-label::before,
-.custom-file-label,
-.custom-file-text,
-.custom-file-button,
-.custom-select {
-  @include transition($custom-forms-transition);
-}
diff --git a/scss/_forms.scss b/scss/_forms.scss
index 0bc66587e9..ff9a016de7 100644
--- a/scss/_forms.scss
+++ b/scss/_forms.scss
@@ -1,334 +1,9 @@
-// stylelint-disable selector-no-qualifying-type
-
-//
-// Textual form controls
-//
-
-.form-control {
-  display: block;
-  width: 100%;
-  height: $input-height;
-  padding: $input-padding-y $input-padding-x;
-  font-family: $input-font-family;
-  @include font-size($input-font-size);
-  font-weight: $input-font-weight;
-  line-height: $input-line-height;
-  color: $input-color;
-  background-color: $input-bg;
-  background-clip: padding-box;
-  border: $input-border-width solid $input-border-color;
-
-  // Note: This has no effect on <select>s in some browsers, due to the limited stylability of `<select>`s in CSS.
-  @include border-radius($input-border-radius, 0);
-
-  @include box-shadow($input-box-shadow);
-  @include transition($input-transition);
-
-  // Unstyle the caret on `<select>`s in IE10+.
-  &::-ms-expand {
-    background-color: transparent;
-    border: 0;
-  }
-
-  // Customize the `:focus` state to imitate native WebKit styles.
-  @include form-control-focus($ignore-warning: true);
-
-  // Placeholder
-  &::placeholder {
-    color: $input-placeholder-color;
-    // Override Firefox's unusual default opacity; see https://github.com/twbs/bootstrap/pull/11526.
-    opacity: 1;
-  }
-
-  // Disabled and read-only inputs
-  //
-  // HTML5 says that controls under a fieldset > legend:first-child won't be
-  // disabled if the fieldset is disabled. Due to implementation difficulty, we
-  // don't honor that edge case; we style them as disabled anyway.
-  &:disabled,
-  &[readonly] {
-    background-color: $input-disabled-bg;
-    // iOS fix for unreadable disabled content; see https://github.com/twbs/bootstrap/issues/11655.
-    opacity: 1;
-  }
-}
-
-select.form-control {
-  &:focus::-ms-value {
-    // Suppress the nested default white text on blue background highlight given to
-    // the selected option text when the (still closed) <select> receives focus
-    // in IE and (under certain conditions) Edge, as it looks bad and cannot be made to
-    // match the appearance of the native widget.
-    // See https://github.com/twbs/bootstrap/issues/19398.
-    color: $input-color;
-    background-color: $input-bg;
-  }
-}
-
-// Make file inputs better match text inputs by forcing them to new lines.
-.form-control-file,
-.form-control-range {
-  display: block;
-  width: 100%;
-}
-
-
-//
-// Labels
-//
-
-// For use with horizontal and inline forms, when you need the label (or legend)
-// text to align with the form controls.
-.col-form-label {
-  padding-top: calc(#{$input-padding-y} + #{$input-border-width});
-  padding-bottom: calc(#{$input-padding-y} + #{$input-border-width});
-  margin-bottom: 0; // Override the `<label>/<legend>` default
-  @include font-size(inherit); // Override the `<legend>` default
-  line-height: $input-line-height;
-}
-
-.col-form-label-lg {
-  padding-top: calc(#{$input-padding-y-lg} + #{$input-border-width});
-  padding-bottom: calc(#{$input-padding-y-lg} + #{$input-border-width});
-  @include font-size($input-font-size-lg);
-  line-height: $input-line-height-lg;
-}
-
-.col-form-label-sm {
-  padding-top: calc(#{$input-padding-y-sm} + #{$input-border-width});
-  padding-bottom: calc(#{$input-padding-y-sm} + #{$input-border-width});
-  @include font-size($input-font-size-sm);
-  line-height: $input-line-height-sm;
-}
-
-
-// Readonly controls as plain text
-//
-// Apply class to a readonly input to make it appear like regular plain
-// text (without any border, background color, focus indicator)
-
-.form-control-plaintext {
-  display: block;
-  width: 100%;
-  padding: $input-padding-y 0;
-  margin-bottom: 0; // match inputs if this class comes on inputs with default margins
-  @include font-size($input-font-size);
-  line-height: $input-line-height;
-  color: $input-plaintext-color;
-  background-color: transparent;
-  border: solid transparent;
-  border-width: $input-border-width 0;
-
-  &.form-control-sm,
-  &.form-control-lg {
-    padding-right: 0;
-    padding-left: 0;
-  }
-}
-
-
-// Form control sizing
-//
-// Build on `.form-control` with modifier classes to decrease or increase the
-// height and font-size of form controls.
-//
-// Repeated in `_input_group.scss` to avoid Sass extend issues.
-
-.form-control-sm {
-  height: $input-height-sm;
-  padding: $input-padding-y-sm $input-padding-x-sm;
-  @include font-size($input-font-size-sm);
-  line-height: $input-line-height-sm;
-  @include border-radius($input-border-radius-sm);
-}
-
-.form-control-lg {
-  height: $input-height-lg;
-  padding: $input-padding-y-lg $input-padding-x-lg;
-  @include font-size($input-font-size-lg);
-  line-height: $input-line-height-lg;
-  @include border-radius($input-border-radius-lg);
-}
-
-// stylelint-disable-next-line no-duplicate-selectors
-select.form-control {
-  &[size],
-  &[multiple] {
-    height: auto;
-  }
-}
-
-textarea.form-control {
-  height: auto;
-}
-
-// Form groups
-//
-// Designed to help with the organization and spacing of vertical forms. For
-// horizontal forms, use the predefined grid classes.
-
-.form-group {
-  margin-bottom: $form-group-margin-bottom;
-}
-
-.form-text {
-  display: block;
-  margin-top: $form-text-margin-top;
-}
-
-
-// Form grid
-//
-// Special replacement for our grid system's `.row` for tighter form layouts.
-
-@if $enable-grid-classes {
-  .form-row {
-    display: flex;
-    flex-wrap: wrap;
-    margin-right: -$form-grid-gutter-width / 2;
-    margin-left: -$form-grid-gutter-width / 2;
-
-    > .col,
-    > [class*="col-"] {
-      padding-right: $form-grid-gutter-width / 2;
-      padding-left: $form-grid-gutter-width / 2;
-    }
-  }
-}
-
-
-// Checkboxes and radios
-//
-// Indent the labels to position radios/checkboxes as hanging controls.
-
-.form-check {
-  position: relative;
-  display: block;
-  padding-left: $form-check-input-gutter;
-}
-
-.form-check-input {
-  position: absolute;
-  margin-top: $form-check-input-margin-y;
-  margin-left: -$form-check-input-gutter;
-
-  // Use disabled attribute instead of :disabled pseudo-class
-  // Workaround for: https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/11295231
-  &[disabled] ~ .form-check-label {
-    color: $text-muted;
-  }
-}
-
-.form-check-label {
-  margin-bottom: 0; // Override default `<label>` bottom margin
-}
-
-.form-check-inline {
-  display: inline-flex;
-  align-items: center;
-  padding-left: 0; // Override base .form-check
-  margin-right: $form-check-inline-margin-x;
-
-  // Undo .form-check-input defaults and add some `margin-right`.
-  .form-check-input {
-    position: static;
-    margin-top: 0;
-    margin-right: $form-check-inline-input-margin-x;
-    margin-left: 0;
-  }
-}
-
-
-// Form validation
-//
-// Provide feedback to users when form field values are valid or invalid. Works
-// primarily for client-side validation via scoped `:invalid` and `:valid`
-// pseudo-classes but also includes `.is-invalid` and `.is-valid` classes for
-// server-side validation.
-
-@each $state, $data in $form-validation-states {
-  @include form-validation-state($state, map-get($data, color), map-get($data, icon));
-}
-
-// Inline forms
-//
-// Make forms appear inline(-block) by adding the `.form-inline` class. Inline
-// forms begin stacked on extra small (mobile) devices and then go inline when
-// viewports reach <768px.
-//
-// Requires wrapping inputs and labels with `.form-group` for proper display of
-// default HTML form controls and our custom form controls (e.g., input groups).
-
-.form-inline {
-  display: flex;
-  flex-flow: row wrap;
-  align-items: center; // Prevent shorter elements from growing to same height as others (e.g., small buttons growing to normal sized button height)
-
-  // Because we use flex, the initial sizing of checkboxes is collapsed and
-  // doesn't occupy the full-width (which is what we want for xs grid tier),
-  // so we force that here.
-  .form-check {
-    width: 100%;
-  }
-
-  // Kick in the inline
-  @include media-breakpoint-up(sm) {
-    label {
-      display: flex;
-      align-items: center;
-      justify-content: center;
-      margin-bottom: 0;
-    }
-
-    // Inline-block all the things for "inline"
-    .form-group {
-      display: flex;
-      flex: 0 0 auto;
-      flex-flow: row wrap;
-      align-items: center;
-      margin-bottom: 0;
-    }
-
-    // Allow folks to *not* use `.form-group`
-    .form-control {
-      display: inline-block;
-      width: auto; // Prevent labels from stacking above inputs in `.form-group`
-      vertical-align: middle;
-    }
-
-    // Make static controls behave like regular ones
-    .form-control-plaintext {
-      display: inline-block;
-    }
-
-    .input-group,
-    .custom-select {
-      width: auto;
-    }
-
-    // Remove default margin on radios/checkboxes that were used for stacking, and
-    // then undo the floating of radios and checkboxes to match.
-    .form-check {
-      display: flex;
-      align-items: center;
-      justify-content: center;
-      width: auto;
-      padding-left: 0;
-    }
-    .form-check-input {
-      position: relative;
-      flex-shrink: 0;
-      margin-top: 0;
-      margin-right: $form-check-input-margin-x;
-      margin-left: 0;
-    }
-
-    .custom-control {
-      align-items: center;
-      justify-content: center;
-    }
-    .custom-control-label {
-      margin-bottom: 0;
-    }
-  }
-}
+@import "forms/labels";
+@import "forms/form-control";
+@import "forms/form-select";
+@import "forms/form-check";
+@import "forms/form-file";
+@import "forms/form-range";
+@import "forms/layout";
+@import "forms/input-group";
+@import "forms/validation";
diff --git a/scss/_reboot.scss b/scss/_reboot.scss
index df3eacbff8..3553c24910 100644
--- a/scss/_reboot.scss
+++ b/scss/_reboot.scss
@@ -158,6 +158,12 @@ address {
 }
 
 ol,
+ul {
+  padding-right: 2rem;
+  padding-left: 2rem;
+}
+
+ol,
 ul,
 dl {
   margin-top: 0;
diff --git a/scss/_tables.scss b/scss/_tables.scss
index 95d1c4a867..d1fbdc21d2 100644
--- a/scss/_tables.scss
+++ b/scss/_tables.scss
@@ -12,12 +12,16 @@
   td {
     padding: $table-cell-padding;
     vertical-align: top;
-    border-top: $table-border-width solid $table-border-color;
+    border-bottom: $table-border-width solid $table-border-color;
+  }
+
+  td {
+    border-bottom: $table-border-width solid $table-border-color;
   }
 
   thead th {
     vertical-align: bottom;
-    border-bottom: (2 * $table-border-width) solid $table-border-color;
+    border-bottom-color: $table-head-border-color;
   }
 
   tbody + tbody {
diff --git a/scss/_variables.scss b/scss/_variables.scss
index 7b28d94ddb..56bd143dbf 100644
--- a/scss/_variables.scss
+++ b/scss/_variables.scss
@@ -351,8 +351,8 @@ $hr-margin-y:                 $spacer !default;
 //
 // Customizes the `.table` component with basic values, each used across all table variations.
 
-$table-cell-padding:          .75rem !default;
-$table-cell-padding-sm:       .3rem !default;
+$table-cell-padding:          .5rem !default;
+$table-cell-padding-sm:       .25rem !default;
 
 $table-color:                 $body-color !default;
 $table-bg:                    null !default;
@@ -366,6 +366,7 @@ $table-border-color:          $border-color !default;
 
 $table-head-bg:               $gray-200 !default;
 $table-head-color:            $gray-700 !default;
+$table-head-border-color:     $gray-700 !default;
 
 $table-dark-color:            $white !default;
 $table-dark-bg:               $gray-800 !default;
@@ -506,17 +507,61 @@ $input-height-lg:                       calc(#{$input-line-height-lg * 1em} + #{
 
 $input-transition:                      border-color .15s ease-in-out, box-shadow .15s ease-in-out !default;
 
+
+$form-check-input-width:                  1.25em !default;
+$form-check-min-height:                   $font-size-base * $line-height-base !default;
+$form-check-padding-left:                 $form-check-input-width + .5em !default;
+$form-check-margin-bottom:                .125rem !default;
+
+$form-check-input-active-filter:          brightness(90%) !default;
+
+$form-check-input-bg:                     $body-bg !default;
+$form-check-input-border:                 1px solid rgba(0, 0, 0, .25) !default;
+$form-check-input-border-radius:          .25em !default;
+$form-check-radio-border-radius:          50% !default;
+$form-check-input-focus-border:           $input-focus-border-color !default;
+$form-check-input-focus-box-shadow:       $input-btn-focus-box-shadow !default;
+
+$form-check-input-checked-color:          $component-active-color !default;
+$form-check-input-checked-bg-color:       $component-active-bg !default;
+$form-check-input-checked-border-color:   $form-check-input-checked-bg-color !default;
+$form-check-input-checked-bg-repeat:      no-repeat !default;
+$form-check-input-checked-bg-position:    center center !default;
+$form-check-input-checked-bg-size:        1em !default;
+$form-check-input-checked-bg-image:       str-replace(url('data:image/svg+xml;utf8,<svg viewbox="0 0 16 16" xmlns="http://www.w3.org/2000/svg"><path stroke="#{$form-check-input-checked-color}" stroke-width="3" d="M4 8.5L6.5 11l6-6" fill="none" fill-rule="evenodd" stroke-linecap="round" stroke-linejoin="round"/></svg>'), "#", "%23") !default;
+$form-check-radio-checked-bg-image: str-replace(url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='-4 -4 8 8'%3e%3ccircle r='3' fill='#{$form-check-input-checked-color}'/%3e%3c/svg%3e"), "#", "%23") !default;
+
+$form-check-input-indeterminate-color:          $component-active-color !default;
+$form-check-input-indeterminate-bg-color:       $component-active-bg !default;
+$form-check-input-indeterminate-border-color:   $form-check-input-indeterminate-bg-color !default;
+$form-check-input-indeterminate-bg-repeat:      no-repeat !default;
+$form-check-input-indeterminate-bg-position:    center center !default;
+$form-check-input-indeterminate-bg-size:        1em !default;
+$form-check-input-indeterminate-bg-image:       str-replace(url('data:image/svg+xml;utf8,<svg viewbox="0 0 16 16" xmlns="http://www.w3.org/2000/svg"><path d="M5 8h6" stroke="#{$form-check-input-indeterminate-color}" stroke-width="3" fill="none" fill-rule="evenodd" stroke-linecap="round" stroke-linejoin="round"/></svg>'), "#", "%23") !default;
+
+$form-switch-color:               rgba(0, 0, 0, .25) !default;
+$form-switch-width:               2em !default;
+$form-switch-height:              $form-check-input-width !default;
+$form-switch-padding-left:        $form-switch-width + .5em !default;
+$form-switch-bg-image:            str-replace(url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='-4 -4 8 8'%3e%3ccircle r='3' fill='#{$form-switch-color}'/%3e%3c/svg%3e"), "#", "%23") !default;
+$form-switch-border-radius:       $form-switch-width !default;
+$form-switch-transition:          .2s ease-in-out !default;
+$form-switch-transition-property: background-position, background-color !default;
+
+$form-switch-focus-color:         hsla(211, 100%, 75%, 1) !default;
+$form-switch-focus-bg-image:      str-replace(url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='-4 -4 8 8'%3e%3ccircle r='3' fill='#{$form-switch-focus-color}'/%3e%3c/svg%3e"), "#", "%23") !default;
+
+$form-switch-checked-color:       $component-active-color !default;
+$form-switch-checked-bg-image:      str-replace(url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='-4 -4 8 8'%3e%3ccircle r='3' fill='#{$form-switch-checked-color}'/%3e%3c/svg%3e"), "#", "%23") !default;
+$form-switch-checked-bg-position:  right center !default;
+
 $form-text-margin-top:                  .25rem !default;
 
-$form-check-input-gutter:               1.25rem !default;
-$form-check-input-margin-y:             .3rem !default;
-$form-check-input-margin-x:             .25rem !default;
+$form-check-inline-margin-right:        1rem !default;
 
-$form-check-inline-margin-x:            .75rem !default;
-$form-check-inline-input-margin-x:      .3125rem !default;
+$form-check-input-margin-x:             .25rem !default;
 
 $form-grid-gutter-width:                10px !default;
-$form-group-margin-bottom:              1rem !default;
 
 $input-group-addon-color:               $input-color !default;
 $input-group-addon-bg:                  $gray-200 !default;
@@ -524,128 +569,83 @@ $input-group-addon-border-color:        $input-border-color !default;
 
 $custom-forms-transition:               background-color .15s ease-in-out, border-color .15s ease-in-out, box-shadow .15s ease-in-out !default;
 
-$custom-control-gutter:                 .5rem !default;
-$custom-control-spacer-x:               1rem !default;
-
-$custom-control-indicator-size:         1rem !default;
-$custom-control-indicator-bg:           $input-bg !default;
-
-$custom-control-indicator-bg-size:      50% 50% !default;
-$custom-control-indicator-box-shadow:   $input-box-shadow !default;
-$custom-control-indicator-border-color: $gray-500 !default;
-$custom-control-indicator-border-width: $input-border-width !default;
-
-$custom-control-label-color:            null !default;
-
-$custom-control-indicator-disabled-bg:          $input-disabled-bg !default;
-$custom-control-label-disabled-color:           $gray-600 !default;
-
-$custom-control-indicator-checked-color:        $component-active-color !default;
-$custom-control-indicator-checked-bg:           $component-active-bg !default;
-$custom-control-indicator-checked-disabled-bg:  rgba(theme-color("primary"), .5) !default;
-$custom-control-indicator-checked-box-shadow:   none !default;
-$custom-control-indicator-checked-border-color: $custom-control-indicator-checked-bg !default;
-
-$custom-control-indicator-focus-box-shadow:     $input-focus-box-shadow !default;
-$custom-control-indicator-focus-border-color:   $input-focus-border-color !default;
-
-$custom-control-indicator-active-color:         $component-active-color !default;
-$custom-control-indicator-active-bg:            lighten($component-active-bg, 35%) !default;
-$custom-control-indicator-active-box-shadow:    none !default;
-$custom-control-indicator-active-border-color:  $custom-control-indicator-active-bg !default;
-
-$custom-checkbox-indicator-border-radius:       $border-radius !default;
-$custom-checkbox-indicator-icon-checked:        str-replace(url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 8 8'%3e%3cpath fill='#{$custom-control-indicator-checked-color}' d='M6.564.75l-3.59 3.612-1.538-1.55L0 4.26 2.974 7.25 8 2.193z'/%3e%3c/svg%3e"), "#", "%23") !default;
-
-$custom-checkbox-indicator-indeterminate-bg:           $component-active-bg !default;
-$custom-checkbox-indicator-indeterminate-color:        $custom-control-indicator-checked-color !default;
-$custom-checkbox-indicator-icon-indeterminate:         str-replace(url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 4 4'%3e%3cpath stroke='#{$custom-checkbox-indicator-indeterminate-color}' d='M0 2h4'/%3e%3c/svg%3e"), "#", "%23") !default;
-$custom-checkbox-indicator-indeterminate-box-shadow:   none !default;
-$custom-checkbox-indicator-indeterminate-border-color: $custom-checkbox-indicator-indeterminate-bg !default;
-
-$custom-radio-indicator-border-radius:          50% !default;
-$custom-radio-indicator-icon-checked:           str-replace(url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='-4 -4 8 8'%3e%3ccircle r='3' fill='#{$custom-control-indicator-checked-color}'/%3e%3c/svg%3e"), "#", "%23") !default;
-
-$custom-switch-width:                           $custom-control-indicator-size * 1.75 !default;
-$custom-switch-indicator-border-radius:         $custom-control-indicator-size / 2 !default;
-$custom-switch-indicator-size:                  calc(#{$custom-control-indicator-size} - #{$custom-control-indicator-border-width * 4}) !default;
-
-$custom-select-padding-y:           $input-padding-y !default;
-$custom-select-padding-x:           $input-padding-x !default;
-$custom-select-font-family:         $input-font-family !default;
-$custom-select-font-size:           $input-font-size !default;
-$custom-select-height:              $input-height !default;
-$custom-select-indicator-padding:   1rem !default; // Extra padding to account for the presence of the background-image based indicator
-$custom-select-font-weight:         $input-font-weight !default;
-$custom-select-line-height:         $input-line-height !default;
-$custom-select-color:               $input-color !default;
-$custom-select-disabled-color:      $gray-600 !default;
-$custom-select-bg:                  $input-bg !default;
-$custom-select-disabled-bg:         $gray-200 !default;
-$custom-select-bg-size:             8px 10px !default; // In pixels because image dimensions
-$custom-select-indicator-color:     $gray-800 !default;
-$custom-select-indicator:           str-replace(url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 4 5'%3e%3cpath fill='#{$custom-select-indicator-color}' d='M2 0L0 2h4zm0 5L0 3h4z'/%3e%3c/svg%3e"), "#", "%23") !default;
-$custom-select-background:          $custom-select-indicator no-repeat right $custom-select-padding-x center / $custom-select-bg-size !default; // Used so we can have multiple background elements (e.g., arrow and feedback icon)
-
-$custom-select-feedback-icon-padding-right: calc((1em + #{2 * $custom-select-padding-y}) * 3 / 4 + #{$custom-select-padding-x + $custom-select-indicator-padding}) !default;
-$custom-select-feedback-icon-position:      center right ($custom-select-padding-x + $custom-select-indicator-padding) !default;
-$custom-select-feedback-icon-size:          $input-height-inner-half $input-height-inner-half !default;
-
-$custom-select-border-width:        $input-border-width !default;
-$custom-select-border-color:        $input-border-color !default;
-$custom-select-border-radius:       $border-radius !default;
-$custom-select-box-shadow:          inset 0 1px 2px rgba($black, .075) !default;
-
-$custom-select-focus-border-color:  $input-focus-border-color !default;
-$custom-select-focus-width:         $input-focus-width !default;
-$custom-select-focus-box-shadow:    0 0 0 $custom-select-focus-width $input-btn-focus-color !default;
-
-$custom-select-padding-y-sm:        $input-padding-y-sm !default;
-$custom-select-padding-x-sm:        $input-padding-x-sm !default;
-$custom-select-font-size-sm:        $input-font-size-sm !default;
-$custom-select-height-sm:           $input-height-sm !default;
-
-$custom-select-padding-y-lg:        $input-padding-y-lg !default;
-$custom-select-padding-x-lg:        $input-padding-x-lg !default;
-$custom-select-font-size-lg:        $input-font-size-lg !default;
-$custom-select-height-lg:           $input-height-lg !default;
-
-$custom-range-track-width:          100% !default;
-$custom-range-track-height:         .5rem !default;
-$custom-range-track-cursor:         pointer !default;
-$custom-range-track-bg:             $gray-300 !default;
-$custom-range-track-border-radius:  1rem !default;
-$custom-range-track-box-shadow:     inset 0 .25rem .25rem rgba($black, .1) !default;
-
-$custom-range-thumb-width:                   1rem !default;
-$custom-range-thumb-height:                  $custom-range-thumb-width !default;
-$custom-range-thumb-bg:                      $component-active-bg !default;
-$custom-range-thumb-border:                  0 !default;
-$custom-range-thumb-border-radius:           1rem !default;
-$custom-range-thumb-box-shadow:              0 .1rem .25rem rgba($black, .1) !default;
-$custom-range-thumb-focus-box-shadow:        0 0 0 1px $body-bg, $input-focus-box-shadow !default;
-$custom-range-thumb-focus-box-shadow-width:  $input-focus-width !default; // For focus box shadow issue in IE/Edge
-$custom-range-thumb-active-bg:               lighten($component-active-bg, 35%) !default;
-$custom-range-thumb-disabled-bg:             $gray-500 !default;
-
-$custom-file-height:                $input-height !default;
-$custom-file-focus-border-color:    $input-focus-border-color !default;
-$custom-file-focus-box-shadow:      $input-focus-box-shadow !default;
-$custom-file-disabled-bg:           $input-disabled-bg !default;
-
-$custom-file-padding-y:             $input-padding-y !default;
-$custom-file-padding-x:             $input-padding-x !default;
-$custom-file-line-height:           $input-line-height !default;
-$custom-file-font-family:           $input-font-family !default;
-$custom-file-font-weight:           $input-font-weight !default;
-$custom-file-color:                 $input-color !default;
-$custom-file-bg:                    $input-bg !default;
-$custom-file-border-width:          $input-border-width !default;
-$custom-file-border-color:          $input-border-color !default;
-$custom-file-border-radius:         $input-border-radius !default;
-$custom-file-box-shadow:            $input-box-shadow !default;
-$custom-file-button-color:          $custom-file-color !default;
-$custom-file-button-bg:             $input-group-addon-bg !default;
+$form-select-padding-y:           $input-padding-y !default;
+$form-select-padding-x:           $input-padding-x !default;
+$form-select-font-family:         $input-font-family !default;
+$form-select-font-size:           $input-font-size !default;
+$form-select-height:              $input-height !default;
+$form-select-indicator-padding:   1rem !default; // Extra padding to account for the presence of the background-image based indicator
+$form-select-font-weight:         $input-font-weight !default;
+$form-select-line-height:         $input-line-height !default;
+$form-select-color:               $input-color !default;
+$form-select-disabled-color:      $gray-600 !default;
+$form-select-bg:                  $input-bg !default;
+$form-select-disabled-bg:         $gray-200 !default;
+$form-select-bg-size:             16px 12px !default; // In pixels because image dimensions
+$form-select-indicator-color:     $gray-800 !default;
+$form-select-indicator:           str-replace(url('data:image/svg+xml;utf8,<svg viewbox="0 0 16 16" xmlns="http://www.w3.org/2000/svg"><path stroke="#{$form-select-indicator-color}" stroke-width="2px" d="M2 5l6 6 6-6" fill="none" fill-rule="evenodd" stroke-linecap="round" stroke-linejoin="round"/></svg>'), "#", "%23") !default;
+
+$form-select-background:          $form-select-indicator no-repeat right $form-select-padding-x center / $form-select-bg-size !default; // Used so we can have multiple background elements (e.g., arrow and feedback icon)
+
+$form-select-feedback-icon-padding-right: calc((1em + #{2 * $form-select-padding-y}) * 3 / 4 + #{$form-select-padding-x + $form-select-indicator-padding}) !default;
+$form-select-feedback-icon-position:      center right ($form-select-padding-x + $form-select-indicator-padding) !default;
+$form-select-feedback-icon-size:          $input-height-inner-half $input-height-inner-half !default;
+
+$form-select-border-width:        $input-border-width !default;
+$form-select-border-color:        $input-border-color !default;
+$form-select-border-radius:       $border-radius !default;
+$form-select-box-shadow:          inset 0 1px 2px rgba($black, .075) !default;
+
+$form-select-focus-border-color:  $input-focus-border-color !default;
+$form-select-focus-width:         $input-focus-width !default;
+$form-select-focus-box-shadow:    0 0 0 $form-select-focus-width $input-btn-focus-color !default;
+
+$form-select-padding-y-sm:        $input-padding-y-sm !default;
+$form-select-padding-x-sm:        $input-padding-x-sm !default;
+$form-select-font-size-sm:        $input-font-size-sm !default;
+$form-select-height-sm:           $input-height-sm !default;
+
+$form-select-padding-y-lg:        $input-padding-y-lg !default;
+$form-select-padding-x-lg:        $input-padding-x-lg !default;
+$form-select-font-size-lg:        $input-font-size-lg !default;
+$form-select-height-lg:           $input-height-lg !default;
+
+$form-range-track-width:          100% !default;
+$form-range-track-height:         .5rem !default;
+$form-range-track-cursor:         pointer !default;
+$form-range-track-bg:             $gray-300 !default;
+$form-range-track-border-radius:  1rem !default;
+$form-range-track-box-shadow:     inset 0 .25rem .25rem rgba($black, .1) !default;
+
+$form-range-thumb-width:                   1rem !default;
+$form-range-thumb-height:                  $form-range-thumb-width !default;
+$form-range-thumb-bg:                      $component-active-bg !default;
+$form-range-thumb-border:                  0 !default;
+$form-range-thumb-border-radius:           1rem !default;
+$form-range-thumb-box-shadow:              0 .1rem .25rem rgba($black, .1) !default;
+$form-range-thumb-focus-box-shadow:        0 0 0 1px $body-bg, $input-focus-box-shadow !default;
+$form-range-thumb-focus-box-shadow-width:  $input-focus-width !default; // For focus box shadow issue in IE/Edge
+$form-range-thumb-active-bg:               lighten($component-active-bg, 35%) !default;
+$form-range-thumb-disabled-bg:             $gray-500 !default;
+
+$form-file-height:                $input-height !default;
+$form-file-focus-border-color:    $input-focus-border-color !default;
+$form-file-focus-box-shadow:      $input-focus-box-shadow !default;
+$form-file-disabled-bg:           $input-disabled-bg !default;
+
+$form-file-padding-y:             $input-padding-y !default;
+$form-file-padding-x:             $input-padding-x !default;
+$form-file-line-height:           $input-line-height !default;
+$form-file-font-family:           $input-font-family !default;
+$form-file-font-weight:           $input-font-weight !default;
+$form-file-color:                 $input-color !default;
+$form-file-bg:                    $input-bg !default;
+$form-file-border-width:          $input-border-width !default;
+$form-file-border-color:          $input-border-color !default;
+$form-file-border-radius:         $input-border-radius !default;
+$form-file-box-shadow:            $input-box-shadow !default;
+$form-file-button-color:          $form-file-color !default;
+$form-file-button-bg:             $input-group-addon-bg !default;
 
 
 // Form validation
diff --git a/scss/bootstrap.scss b/scss/bootstrap.scss
index 6ded9f628f..df1d49e2ad 100644
--- a/scss/bootstrap.scss
+++ b/scss/bootstrap.scss
@@ -27,8 +27,6 @@
 @import "transitions";
 @import "dropdown";
 @import "button-group";
-@import "input-group";
-@import "custom-forms";
 @import "nav";
 @import "navbar";
 @import "card";
diff --git a/scss/forms/_form-check.scss b/scss/forms/_form-check.scss
new file mode 100644
index 0000000000..b309d2e704
--- /dev/null
+++ b/scss/forms/_form-check.scss
@@ -0,0 +1,116 @@
+//
+// Check/radio
+//
+
+.form-check {
+  display: block;
+  min-height: $form-check-min-height;
+  padding-left: $form-check-padding-left;
+  margin-bottom: $form-check-margin-bottom;
+}
+
+.form-check-input {
+  float: left;
+  width: $form-check-input-width;
+  height: $form-check-input-width;
+  // Todo: Change static value to base line-height?
+  margin-top: calc((1.5em - #{$form-check-input-width}) / 2); // line-height minus check height
+  margin-left: $form-check-padding-left * -1;
+  background-color: $form-check-input-bg;
+  border: $form-check-input-border;
+  appearance: none;
+
+  &[type="checkbox"] {
+    @include border-radius($form-check-input-border-radius);
+  }
+
+  &[type="radio"] {
+    @include border-radius($form-check-radio-border-radius);
+  }
+
+  &:active {
+    filter: $form-check-input-active-filter;
+  }
+
+  &:focus {
+    border-color: $form-check-input-focus-border;
+    outline: 0;
+    box-shadow: $form-check-input-focus-box-shadow;
+  }
+
+  &:checked {
+    background-color: $form-check-input-checked-bg-color;
+    background-repeat: $form-check-input-checked-bg-repeat;
+    background-position: $form-check-input-checked-bg-position;
+    background-size: $form-check-input-checked-bg-size;
+    border-color: $form-check-input-checked-border-color;
+
+    &[type="checkbox"] {
+      background-image: $form-check-input-checked-bg-image;
+    }
+
+    &[type="radio"] {
+      background-image: $form-check-radio-checked-bg-image;
+    }
+  }
+
+  &[type="checkbox"]:indeterminate {
+    background-color: $form-check-input-indeterminate-bg-color;
+    background-image: $form-check-input-indeterminate-bg-image;
+    background-repeat: $form-check-input-indeterminate-bg-repeat;
+    background-position: $form-check-input-indeterminate-bg-position;
+    background-size: $form-check-input-indeterminate-bg-size;
+    border-color: $form-check-input-indeterminate-border-color;
+  }
+
+  // Use disabled attribute instead of :disabled pseudo-class
+  // Workaround for: https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/11295231
+  &[disabled] {
+    pointer-events: none;
+    filter: none;
+    opacity: .5;
+
+    ~ .form-check-label {
+      opacity: .5;
+    }
+  }
+}
+
+.form-check-label {
+  margin-bottom: 0;
+}
+
+//
+// Switch
+//
+
+.form-switch {
+  padding-left: $form-switch-padding-left;
+
+  .form-check-input {
+    width: $form-switch-width;
+    margin-left: $form-switch-padding-left * -1;
+    background-image: $form-switch-bg-image;
+    background-repeat: no-repeat;
+    background-position: left center;
+    background-size: calc(#{$form-switch-height} - 2px); // Get a 1px separation
+    @include border-radius($form-switch-border-radius);
+    // Todo: Figure out how to tackle these, with or without mixin?
+    // transition: $form-switch-transition;
+    // transition-property: $form-switch-transition-property;
+
+    &:focus {
+      background-image: $form-switch-focus-bg-image;
+    }
+
+    &:checked {
+      background-image: $form-switch-checked-bg-image;
+      background-position: $form-switch-checked-bg-position;
+    }
+  }
+}
+
+.form-check-inline {
+  display: inline-block;
+  margin-right: $form-check-inline-margin-right;
+}
diff --git a/scss/forms/_form-control.scss b/scss/forms/_form-control.scss
new file mode 100644
index 0000000000..ce2b426627
--- /dev/null
+++ b/scss/forms/_form-control.scss
@@ -0,0 +1,115 @@
+// stylelint-disable selector-no-qualifying-type
+
+//
+// Textual form controls
+//
+
+.form-control {
+  display: block;
+  width: 100%;
+  height: $input-height;
+  padding: $input-padding-y $input-padding-x;
+  font-family: $input-font-family;
+  @include font-size($input-font-size);
+  font-weight: $input-font-weight;
+  line-height: $input-line-height;
+  color: $input-color;
+  background-color: $input-bg;
+  background-clip: padding-box;
+  border: $input-border-width solid $input-border-color;
+
+  // Note: This has no effect on <select>s in some browsers, due to the limited stylability of `<select>`s in CSS.
+  @include border-radius($input-border-radius, 0);
+
+  @include box-shadow($input-box-shadow);
+  @include transition($input-transition);
+
+  // Unstyle the caret on `<select>`s in IE10+.
+  &::-ms-expand {
+    background-color: transparent;
+    border: 0;
+  }
+
+  // Customize the `:focus` state to imitate native WebKit styles.
+  &:focus {
+    color: $input-focus-color;
+    background-color: $input-focus-bg;
+    border-color: $input-focus-border-color;
+    outline: 0;
+    // Avoid using mixin so we can pass custom focus shadow properly
+    @if $enable-shadows {
+      box-shadow: $input-box-shadow, $input-focus-box-shadow;
+    } @else {
+      box-shadow: $input-focus-box-shadow;
+    }
+  }
+
+  // Placeholder
+  &::placeholder {
+    color: $input-placeholder-color;
+    // Override Firefox's unusual default opacity; see https://github.com/twbs/bootstrap/pull/11526.
+    opacity: 1;
+  }
+
+  // Disabled and read-only inputs
+  //
+  // HTML5 says that controls under a fieldset > legend:first-child won't be
+  // disabled if the fieldset is disabled. Due to implementation difficulty, we
+  // don't honor that edge case; we style them as disabled anyway.
+  &:disabled,
+  &[readonly] {
+    background-color: $input-disabled-bg;
+    // iOS fix for unreadable disabled content; see https://github.com/twbs/bootstrap/issues/11655.
+    opacity: 1;
+  }
+}
+
+// Readonly controls as plain text
+//
+// Apply class to a readonly input to make it appear like regular plain
+// text (without any border, background color, focus indicator)
+
+.form-control-plaintext {
+  display: block;
+  width: 100%;
+  padding: $input-padding-y 0;
+  margin-bottom: 0; // match inputs if this class comes on inputs with default margins
+  line-height: $input-line-height;
+  color: $input-plaintext-color;
+  background-color: transparent;
+  border: solid transparent;
+  border-width: $input-border-width 0;
+
+  &.form-control-sm,
+  &.form-control-lg {
+    padding-right: 0;
+    padding-left: 0;
+  }
+}
+
+// Form control sizing
+//
+// Build on `.form-control` with modifier classes to decrease or increase the
+// height and font-size of form controls.
+//
+// Repeated in `_input_group.scss` to avoid Sass extend issues.
+
+.form-control-sm {
+  height: $input-height-sm;
+  padding: $input-padding-y-sm $input-padding-x-sm;
+  @include font-size($input-font-size-sm);
+  line-height: $input-line-height-sm;
+  @include border-radius($input-border-radius-sm);
+}
+
+.form-control-lg {
+  height: $input-height-lg;
+  padding: $input-padding-y-lg $input-padding-x-lg;
+  @include font-size($input-font-size-lg);
+  line-height: $input-line-height-lg;
+  @include border-radius($input-border-radius-lg);
+}
+
+textarea.form-control {
+  height: auto;
+}
diff --git a/scss/forms/_form-file.scss b/scss/forms/_form-file.scss
new file mode 100644
index 0000000000..bbc38a9f81
--- /dev/null
+++ b/scss/forms/_form-file.scss
@@ -0,0 +1,72 @@
+.form-file {
+  position: relative;
+  display: inline-block;
+  width: 100%;
+  height: $form-file-height;
+  margin-bottom: 0;
+}
+
+.form-file-input {
+  position: relative;
+  z-index: 2;
+  width: 100%;
+  height: $form-file-height;
+  margin: 0;
+  opacity: 0;
+
+  &:focus ~ .form-file-label {
+    border-color: $form-file-focus-border-color;
+    box-shadow: $form-file-focus-box-shadow;
+  }
+
+  // Use disabled attribute instead of :disabled pseudo-class
+  // Workaround for: https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/11295231
+  &[disabled] ~ .form-file-label {
+    background-color: $form-file-disabled-bg;
+  }
+}
+
+.form-file-label {
+  position: absolute;
+  top: 0;
+  right: 0;
+  left: 0;
+  z-index: 1;
+  display: flex;
+  height: $form-file-height;
+  border-color: $form-file-border-color;
+  @include border-radius($form-file-border-radius);
+  @include box-shadow($form-file-box-shadow);
+}
+
+.form-file-text {
+  display: block;
+  flex-grow: 1;
+  padding: $form-file-padding-y $form-file-padding-x;
+  overflow: hidden;
+  font-family: $form-file-font-family;
+  font-weight: $form-file-font-weight;
+  line-height: $form-file-line-height;
+  color: $form-file-color;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  background-color: $form-file-bg;
+  border-color: inherit;
+  border-style: solid;
+  border-width: $form-file-border-width;
+  @include border-left-radius(inherit);
+}
+
+.form-file-button {
+  display: block;
+  flex-shrink: 0;
+  padding: $form-file-padding-y $form-file-padding-x;
+  margin-left: -$form-file-border-width;
+  line-height: $form-file-line-height;
+  color: $form-file-button-color;
+  @include gradient-bg($form-file-button-bg);
+  border-color: inherit;
+  border-style: solid;
+  border-width: $form-file-border-width;
+  @include border-right-radius(inherit);
+}
diff --git a/scss/forms/_form-range.scss b/scss/forms/_form-range.scss
new file mode 100644
index 0000000000..b54d4d6aaf
--- /dev/null
+++ b/scss/forms/_form-range.scss
@@ -0,0 +1,142 @@
+// Range
+//
+// Style range inputs the same across browsers. Vendor-specific rules for pseudo
+// elements cannot be mixed. As such, there are no shared styles for focus or
+// active states on prefixed selectors.
+
+.form-range {
+  width: 100%;
+  height: calc(#{$form-range-thumb-height} + #{$form-range-thumb-focus-box-shadow-width * 2});
+  padding: 0; // Need to reset padding
+  background-color: transparent;
+  appearance: none;
+
+  &:focus {
+    outline: none;
+
+    // Pseudo-elements must be split across multiple rulesets to have an effect.
+    // No box-shadow() mixin for focus accessibility.
+    &::-webkit-slider-thumb { box-shadow: $form-range-thumb-focus-box-shadow; }
+    &::-moz-range-thumb     { box-shadow: $form-range-thumb-focus-box-shadow; }
+    &::-ms-thumb            { box-shadow: $form-range-thumb-focus-box-shadow; }
+  }
+
+  &::-moz-focus-outer {
+    border: 0;
+  }
+
+  &::-webkit-slider-thumb {
+    width: $form-range-thumb-width;
+    height: $form-range-thumb-height;
+    margin-top: ($form-range-track-height - $form-range-thumb-height) / 2; // Webkit specific
+    @include gradient-bg($form-range-thumb-bg);
+    border: $form-range-thumb-border;
+    @include border-radius($form-range-thumb-border-radius);
+    @include box-shadow($form-range-thumb-box-shadow);
+    @include transition($custom-forms-transition);
+    appearance: none;
+
+    &:active {
+      @include gradient-bg($form-range-thumb-active-bg);
+    }
+  }
+
+  &::-webkit-slider-runnable-track {
+    width: $form-range-track-width;
+    height: $form-range-track-height;
+    color: transparent; // Why?
+    cursor: $form-range-track-cursor;
+    background-color: $form-range-track-bg;
+    border-color: transparent;
+    @include border-radius($form-range-track-border-radius);
+    @include box-shadow($form-range-track-box-shadow);
+  }
+
+  &::-moz-range-thumb {
+    width: $form-range-thumb-width;
+    height: $form-range-thumb-height;
+    @include gradient-bg($form-range-thumb-bg);
+    border: $form-range-thumb-border;
+    @include border-radius($form-range-thumb-border-radius);
+    @include box-shadow($form-range-thumb-box-shadow);
+    @include transition($custom-forms-transition);
+    appearance: none;
+
+    &:active {
+      @include gradient-bg($form-range-thumb-active-bg);
+    }
+  }
+
+  &::-moz-range-track {
+    width: $form-range-track-width;
+    height: $form-range-track-height;
+    color: transparent;
+    cursor: $form-range-track-cursor;
+    background-color: $form-range-track-bg;
+    border-color: transparent; // Firefox specific?
+    @include border-radius($form-range-track-border-radius);
+    @include box-shadow($form-range-track-box-shadow);
+  }
+
+  &::-ms-thumb {
+    width: $form-range-thumb-width;
+    height: $form-range-thumb-height;
+    margin-top: 0; // Edge specific
+    margin-right: $form-range-thumb-focus-box-shadow-width; // Workaround that overflowed box-shadow is hidden.
+    margin-left: $form-range-thumb-focus-box-shadow-width;  // Workaround that overflowed box-shadow is hidden.
+    @include gradient-bg($form-range-thumb-bg);
+    border: $form-range-thumb-border;
+    @include border-radius($form-range-thumb-border-radius);
+    @include box-shadow($form-range-thumb-box-shadow);
+    @include transition($custom-forms-transition);
+    appearance: none;
+
+    &:active {
+      @include gradient-bg($form-range-thumb-active-bg);
+    }
+  }
+
+  &::-ms-track {
+    width: $form-range-track-width;
+    height: $form-range-track-height;
+    color: transparent;
+    cursor: $form-range-track-cursor;
+    background-color: transparent;
+    border-color: transparent;
+    border-width: $form-range-thumb-height / 2;
+    @include box-shadow($form-range-track-box-shadow);
+  }
+
+  &::-ms-fill-lower {
+    background-color: $form-range-track-bg;
+    @include border-radius($form-range-track-border-radius);
+  }
+
+  &::-ms-fill-upper {
+    margin-right: 15px; // arbitrary?
+    background-color: $form-range-track-bg;
+    @include border-radius($form-range-track-border-radius);
+  }
+
+  &:disabled {
+    &::-webkit-slider-thumb {
+      background-color: $form-range-thumb-disabled-bg;
+    }
+
+    &::-webkit-slider-runnable-track {
+      cursor: default;
+    }
+
+    &::-moz-range-thumb {
+      background-color: $form-range-thumb-disabled-bg;
+    }
+
+    &::-moz-range-track {
+      cursor: default;
+    }
+
+    &::-ms-thumb {
+      background-color: $form-range-thumb-disabled-bg;
+    }
+  }
+}
diff --git a/scss/forms/_form-select.scss b/scss/forms/_form-select.scss
new file mode 100644
index 0000000000..e0b69c04f7
--- /dev/null
+++ b/scss/forms/_form-select.scss
@@ -0,0 +1,76 @@
+// Select
+//
+// Replaces the browser default select with a custom one, mostly pulled from
+// https://primer.github.io/.
+
+.form-select {
+  display: inline-block;
+  width: 100%;
+  height: $form-select-height;
+  padding: $form-select-padding-y ($form-select-padding-x + $form-select-indicator-padding) $form-select-padding-y $form-select-padding-x;
+  font-family: $form-select-font-family;
+  @include font-size($form-select-font-size);
+  font-weight: $form-select-font-weight;
+  line-height: $form-select-line-height;
+  color: $form-select-color;
+  vertical-align: middle;
+  background: $form-select-background;
+  background-color: $form-select-bg;
+  border: $form-select-border-width solid $form-select-border-color;
+  @include border-radius($form-select-border-radius, 0);
+  @include box-shadow($form-select-box-shadow);
+  appearance: none;
+
+  &:focus {
+    border-color: $form-select-focus-border-color;
+    outline: 0;
+    @if $enable-shadows {
+      box-shadow: $form-select-box-shadow, $form-select-focus-box-shadow;
+    } @else {
+      box-shadow: $form-select-focus-box-shadow;
+    }
+
+    &::-ms-value {
+      // For visual consistency with other platforms/browsers,
+      // suppress the default white text on blue background highlight given to
+      // the selected option text when the (still closed) <select> receives focus
+      // in IE and (under certain conditions) Edge.
+      // See https://github.com/twbs/bootstrap/issues/19398.
+      color: $input-color;
+      background-color: $input-bg;
+    }
+  }
+
+  &[multiple],
+  &[size]:not([size="1"]) {
+    height: auto;
+    padding-right: $form-select-padding-x;
+    background-image: none;
+  }
+
+  &:disabled {
+    color: $form-select-disabled-color;
+    background-color: $form-select-disabled-bg;
+  }
+
+  // Hides the default caret in IE11
+  &::-ms-expand {
+    display: none;
+  }
+}
+
+.form-select-sm {
+  height: $form-select-height-sm;
+  padding-top: $form-select-padding-y-sm;
+  padding-bottom: $form-select-padding-y-sm;
+  padding-left: $form-select-padding-x-sm;
+  @include font-size($form-select-font-size-sm);
+}
+
+.form-select-lg {
+  height: $form-select-height-lg;
+  padding-top: $form-select-padding-y-lg;
+  padding-bottom: $form-select-padding-y-lg;
+  padding-left: $form-select-padding-x-lg;
+  @include font-size($form-select-font-size-lg);
+}
diff --git a/scss/_input-group.scss b/scss/forms/_input-group.scss
index c4daddf0c4..099accecba 100644
--- a/scss/_input-group.scss
+++ b/scss/forms/_input-group.scss
@@ -12,45 +12,45 @@
   width: 100%;
 
   > .form-control,
-  > .custom-select,
-  > .custom-file {
+  > .form-select,
+  > .form-file {
     position: relative; // For focus state's z-index
     flex: 1 1 0%;
     margin-bottom: 0;
 
     + .form-control,
-    + .custom-select,
-    + .custom-file {
+    + .form-select,
+    + .form-file {
       margin-left: -$input-border-width;
     }
   }
 
   // Bring the "active" form control to the top of surrounding elements
   > .form-control:focus,
-  > .custom-select:focus,
-  > .custom-file .custom-file-input:focus ~ .custom-file-label {
+  > .form-select:focus,
+  > .form-file .form-file-input:focus ~ .form-file-label {
     z-index: 3;
   }
 
   // Bring the custom file input above the label
-  > .custom-file .custom-file-input:focus {
+  > .form-file .form-file-input:focus {
     z-index: 4;
   }
 
   > .form-control,
-  > .custom-select {
+  > .form-select {
     &:not(:last-child) { @include border-right-radius(0); }
     &:not(:first-child) { @include border-left-radius(0); }
   }
 
   // Custom file inputs have more complex markup, thus requiring different
   // border-radius overrides.
-  > .custom-file {
+  > .form-file {
     display: flex;
     align-items: center;
 
-    &:not(:last-child) .custom-file-label { @include border-right-radius(0); }
-    &:not(:first-child) .custom-file-label { @include border-left-radius(0); }
+    &:not(:last-child) .form-file-label { @include border-right-radius(0); }
+    &:not(:first-child) .form-file-label { @include border-left-radius(0); }
   }
 }
 
@@ -123,12 +123,12 @@
 // manipulation.
 
 .input-group-lg > .form-control:not(textarea),
-.input-group-lg > .custom-select {
+.input-group-lg > .form-select {
   height: $input-height-lg;
 }
 
 .input-group-lg > .form-control,
-.input-group-lg > .custom-select,
+.input-group-lg > .form-select,
 .input-group-lg > .input-group-prepend > .input-group-text,
 .input-group-lg > .input-group-append > .input-group-text,
 .input-group-lg > .input-group-prepend > .btn,
@@ -140,12 +140,12 @@
 }
 
 .input-group-sm > .form-control:not(textarea),
-.input-group-sm > .custom-select {
+.input-group-sm > .form-select {
   height: $input-height-sm;
 }
 
 .input-group-sm > .form-control,
-.input-group-sm > .custom-select,
+.input-group-sm > .form-select,
 .input-group-sm > .input-group-prepend > .input-group-text,
 .input-group-sm > .input-group-append > .input-group-text,
 .input-group-sm > .input-group-prepend > .btn,
@@ -156,9 +156,9 @@
   @include border-radius($input-border-radius-sm);
 }
 
-.input-group-lg > .custom-select,
-.input-group-sm > .custom-select {
-  padding-right: $custom-select-padding-x + $custom-select-indicator-padding;
+.input-group-lg > .form-select,
+.input-group-sm > .form-select {
+  padding-right: $form-select-padding-x + $form-select-indicator-padding;
 }
 
 
diff --git a/scss/forms/_labels.scss b/scss/forms/_labels.scss
new file mode 100644
index 0000000000..1a4ea8c5c8
--- /dev/null
+++ b/scss/forms/_labels.scss
@@ -0,0 +1,27 @@
+//
+// Labels
+//
+
+// For use with horizontal and inline forms, when you need the label (or legend)
+// text to align with the form controls.
+.col-form-label {
+  padding-top: calc(#{$input-padding-y} + #{$input-border-width});
+  padding-bottom: calc(#{$input-padding-y} + #{$input-border-width});
+  margin-bottom: 0; // Override the `<label>/<legend>` default
+  @include font-size(inherit); // Override the `<legend>` default
+  line-height: $input-line-height;
+}
+
+.col-form-label-lg {
+  padding-top: calc(#{$input-padding-y-lg} + #{$input-border-width});
+  padding-bottom: calc(#{$input-padding-y-lg} + #{$input-border-width});
+  @include font-size($input-font-size-lg);
+  line-height: $input-line-height-lg;
+}
+
+.col-form-label-sm {
+  padding-top: calc(#{$input-padding-y-sm} + #{$input-border-width});
+  padding-bottom: calc(#{$input-padding-y-sm} + #{$input-border-width});
+  @include font-size($input-font-size-sm);
+  line-height: $input-line-height-sm;
+}
diff --git a/scss/forms/_layout.scss b/scss/forms/_layout.scss
new file mode 100644
index 0000000000..f65b5493f2
--- /dev/null
+++ b/scss/forms/_layout.scss
@@ -0,0 +1,101 @@
+// Form grid
+//
+// Special replacement for our grid system's `.row` for tighter form layouts.
+
+@if $enable-grid-classes {
+  .form-row {
+    display: flex;
+    flex-wrap: wrap;
+    margin-right: -$form-grid-gutter-width / 2;
+    margin-left: -$form-grid-gutter-width / 2;
+
+    > .col,
+    > [class*="col-"] {
+      padding-right: $form-grid-gutter-width / 2;
+      padding-left: $form-grid-gutter-width / 2;
+    }
+  }
+}
+
+// Inline forms
+//
+// Make forms appear inline(-block) by adding the `.form-inline` class. Inline
+// forms begin stacked on extra small (mobile) devices and then go inline when
+// viewports reach <768px.
+//
+// Requires wrapping inputs and labels with `.form-group` for proper display of
+// default HTML form controls and our custom form controls (e.g., input groups).
+
+.form-inline {
+  display: flex;
+  flex-flow: row wrap;
+  align-items: center; // Prevent shorter elements from growing to same height as others (e.g., small buttons growing to normal sized button height)
+
+  // Because we use flex, the initial sizing of checkboxes is collapsed and
+  // doesn't occupy the full-width (which is what we want for xs grid tier),
+  // so we force that here.
+  .form-check {
+    width: 100%;
+  }
+
+  // Kick in the inline
+  @include media-breakpoint-up(sm) {
+    label {
+      display: flex;
+      align-items: center;
+      justify-content: center;
+      margin-bottom: 0;
+    }
+
+    // Inline-block all the things for "inline"
+    .form-group {
+      display: flex;
+      flex: 0 0 auto;
+      flex-flow: row wrap;
+      align-items: center;
+      margin-bottom: 0;
+    }
+
+    // Allow folks to *not* use `.form-group`
+    .form-control {
+      display: inline-block;
+      width: auto; // Prevent labels from stacking above inputs in `.form-group`
+      vertical-align: middle;
+    }
+
+    // Make static controls behave like regular ones
+    .form-control-plaintext {
+      display: inline-block;
+    }
+
+    .input-group,
+    .form-select {
+      width: auto;
+    }
+
+    // Remove default margin on radios/checkboxes that were used for stacking, and
+    // then undo the floating of radios and checkboxes to match.
+    .form-check {
+      display: flex;
+      align-items: center;
+      justify-content: center;
+      width: auto;
+      padding-left: 0;
+    }
+    .form-check-input {
+      position: relative;
+      flex-shrink: 0;
+      margin-top: 0;
+      margin-right: $form-check-input-margin-x;
+      margin-left: 0;
+    }
+
+    .custom-control {
+      align-items: center;
+      justify-content: center;
+    }
+    .custom-control-label {
+      margin-bottom: 0;
+    }
+  }
+}
diff --git a/scss/forms/_validation.scss b/scss/forms/_validation.scss
new file mode 100644
index 0000000000..d15e20899e
--- /dev/null
+++ b/scss/forms/_validation.scss
@@ -0,0 +1,10 @@
+// Form validation
+//
+// Provide feedback to users when form field values are valid or invalid. Works
+// primarily for client-side validation via scoped `:invalid` and `:valid`
+// pseudo-classes but also includes `.is-invalid` and `.is-valid` classes for
+// server-side validation.
+
+@each $state, $data in $form-validation-states {
+  @include form-validation-state($state, map-get($data, color), map-get($data, icon));
+}
diff --git a/scss/mixins/_forms.scss b/scss/mixins/_forms.scss
index 202663daa4..2001ae0e25 100644
--- a/scss/mixins/_forms.scss
+++ b/scss/mixins/_forms.scss
@@ -97,13 +97,13 @@
     }
   }
 
-  .custom-select {
+  .form-select {
     @include form-validation-state-selector($state) {
       border-color: $color;
 
       @if $enable-validation-icons {
-        padding-right: $custom-select-feedback-icon-padding-right;
-        background: $custom-select-background, $icon $custom-select-bg no-repeat $custom-select-feedback-icon-position / $custom-select-feedback-icon-size;
+        padding-right: $form-select-feedback-icon-padding-right;
+        background: $form-select-background, $icon $form-select-bg no-repeat $form-select-feedback-icon-position / $form-select-feedback-icon-size;
       }
 
       &:focus {
@@ -130,55 +130,36 @@
 
   .form-check-input {
     @include form-validation-state-selector($state) {
-      ~ .form-check-label {
-        color: $color;
+      border-color: $color;
+
+      &:checked {
+        @include gradient-bg(lighten($color, 10%));
       }
 
-      ~ .#{$state}-feedback,
-      ~ .#{$state}-tooltip {
-        display: block;
+      &:focus {
+        box-shadow: 0 0 0 $input-focus-width rgba($color, .25);
       }
-    }
-  }
 
-  .custom-control-input {
-    @include form-validation-state-selector($state) {
-      ~ .custom-control-label {
+      ~ .form-check-label {
         color: $color;
-
-        &::before {
-          border-color: $color;
-        }
       }
 
       ~ .#{$state}-feedback,
       ~ .#{$state}-tooltip {
         display: block;
       }
-
-      &:checked {
-        ~ .custom-control-label::before {
-          border-color: lighten($color, 10%);
-          @include gradient-bg(lighten($color, 10%));
-        }
-      }
-
-      &:focus {
-        ~ .custom-control-label::before {
-          box-shadow: 0 0 0 $input-focus-width rgba($color, .25);
-        }
-
-        &:not(:checked) ~ .custom-control-label::before {
-          border-color: $color;
-        }
-      }
+    }
+  }
+  .form-check-inline .form-check-input {
+    ~ .#{$state}-feedback {
+      margin-left: .5em;
     }
   }
 
   // custom file
-  .custom-file-input {
+  .form-file-input {
     @include form-validation-state-selector($state) {
-      ~ .custom-file-label {
+      ~ .form-file-label {
         border-color: $color;
       }
 
@@ -188,7 +169,7 @@
       }
 
       &:focus {
-        ~ .custom-file-label {
+        ~ .form-file-label {
           border-color: $color;
           box-shadow: 0 0 0 $input-focus-width rgba($color, .25);
         }