Improves forms migration guide, docs, and scss (#24348)

* fixes migration forms guides

* removes container from Horizontal form

* adds col-form-label sizes on form docs

* removes .form-control-label from forms.scss

* add note to migration

2 files changed, 73 insertions, 47 deletions

diff --git a/docs/4.0/components/forms.md b/docs/4.0/components/forms.md
index ba56338506..84891d8417 100644
--- a/docs/4.0/components/forms.md
+++ b/docs/4.0/components/forms.md
@@ -365,62 +365,87 @@ Create horizontal forms with the grid by adding the `.row` class to form groups
 Be sure to add `.col-form-label` to your `<label>`s as well so they're vertically centered with their associated form controls. For `<legend>` elements, you can use `.col-form-legend` to make them appear similar to regular `<label>` elements.
 
 {% example html %}
-<div class="container">
-  <form>
-    <div class="form-group row">
-      <label for="inputEmail3" class="col-sm-2 col-form-label">Email</label>
-      <div class="col-sm-10">
-        <input type="email" class="form-control" id="inputEmail3" placeholder="Email">
-      </div>
+<form>
+  <div class="form-group row">
+    <label for="inputEmail3" class="col-sm-2 col-form-label">Email</label>
+    <div class="col-sm-10">
+      <input type="email" class="form-control" id="inputEmail3" placeholder="Email">
     </div>
-    <div class="form-group row">
-      <label for="inputPassword3" class="col-sm-2 col-form-label">Password</label>
-      <div class="col-sm-10">
-        <input type="password" class="form-control" id="inputPassword3" placeholder="Password">
-      </div>
+  </div>
+  <div class="form-group row">
+    <label for="inputPassword3" class="col-sm-2 col-form-label">Password</label>
+    <div class="col-sm-10">
+      <input type="password" class="form-control" id="inputPassword3" placeholder="Password">
     </div>
-    <fieldset class="form-group">
-      <div class="row">
-        <legend class="col-form-legend col-sm-2">Radios</legend>
-        <div class="col-sm-10">
-          <div class="form-check">
-            <label class="form-check-label">
-              <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios1" value="option1" checked>
-              Option one is this and that&mdash;be sure to include why it's great
-            </label>
-          </div>
-          <div class="form-check">
-            <label class="form-check-label">
-              <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios2" value="option2">
-              Option two can be something else and selecting it will deselect option one
-            </label>
-          </div>
-          <div class="form-check disabled">
-            <label class="form-check-label">
-              <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios3" value="option3" disabled>
-              Option three is disabled
-            </label>
-          </div>
-        </div>
-      </div>
-    </fieldset>
-    <div class="form-group row">
-      <div class="col-sm-2">Checkbox</div>
+  </div>
+  <fieldset class="form-group">
+    <div class="row">
+      <legend class="col-form-legend col-sm-2">Radios</legend>
       <div class="col-sm-10">
         <div class="form-check">
           <label class="form-check-label">
-            <input class="form-check-input" type="checkbox"> Check me out
+            <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios1" value="option1" checked>
+            Option one is this and that&mdash;be sure to include why it's great
+          </label>
+        </div>
+        <div class="form-check">
+          <label class="form-check-label">
+            <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios2" value="option2">
+            Option two can be something else and selecting it will deselect option one
+          </label>
+        </div>
+        <div class="form-check disabled">
+          <label class="form-check-label">
+            <input class="form-check-input" type="radio" name="gridRadios" id="gridRadios3" value="option3" disabled>
+            Option three is disabled
           </label>
         </div>
       </div>
     </div>
-    <div class="form-group row">
-      <div class="col-sm-10">
-        <button type="submit" class="btn btn-primary">Sign in</button>
+  </fieldset>
+  <div class="form-group row">
+    <div class="col-sm-2">Checkbox</div>
+    <div class="col-sm-10">
+      <div class="form-check">
+        <label class="form-check-label">
+          <input class="form-check-input" type="checkbox"> Check me out
+        </label>
       </div>
     </div>
-  </form>
-</div>
+  </div>
+  <div class="form-group row">
+    <div class="col-sm-10">
+      <button type="submit" class="btn btn-primary">Sign in</button>
+    </div>
+  </div>
+</form>
+{% endexample %}
+
+##### Horizontal form label sizing
+
+Be sure to use `.col-form-label-sm` or `.col-form-label-lg` to your `<label>`s to correctly follow the size of `.form-control-lg` and `.form-control-sm`.
+
+{% example html %}
+<form>
+  <div class="form-group row">
+    <label for="colFormLabelSm" class="col-sm-2 col-form-label col-form-label-sm">Email</label>
+    <div class="col-sm-10">
+      <input type="email" class="form-control form-control-sm" id="colFormLabelSm" placeholder="col-form-label-sm">
+    </div>
+  </div>
+  <div class="form-group row">
+    <label for="colFormLabel" class="col-sm-2 col-form-label">Email</label>
+    <div class="col-sm-10">
+      <input type="email" class="form-control" id="colFormLabel" placeholder="col-form-label">
+    </div>
+  </div>
+  <div class="form-group row">
+    <label for="colFormLabelLg" class="col-sm-2 col-form-label col-form-label-lg">Email</label>
+    <div class="col-sm-10">
+      <input type="email" class="form-control form-control-lg" id="colFormLabelLg" placeholder="col-form-label-lg">
+    </div>
+  </div>
+</form>
 {% endexample %}
 
 #### Column sizing
diff --git a/docs/4.0/migration.md b/docs/4.0/migration.md
index 5274e3c4be..bad3738a29 100644
--- a/docs/4.0/migration.md
+++ b/docs/4.0/migration.md
@@ -18,6 +18,7 @@ While in beta, we aim to have no breaking changes. However, things don't always
 - Responsive tables now generate classes for each grid breakpoint. This breaks from Beta 1 in that the `.table-responsive` you've been using is more like `.table-responsive-md`. You may now use `.table-responsive` or `.table-responsive-{sm,md,lg,xl}` as needed.
 - Dropped Bower support as the package manager has been deprecated for alternatives (e.g., Yarn or npm). [See bower/bower#2298](https://github.com/bower/bower/issues/2298) for details.
 - Bootstrap now requires jQuery 3.0.0 or higher.
+- Removed the unused `.form-control-label` class. If you did make use of this class, it was duplicate of the `.col-form-label` class that vertically centered a `<label>` with it's associated input in horizontal form layouts.
 - Changed the `color-yiq` from a mixin that included the `color` property to a function that returns a value, allowing you to use it for any CSS property. For example, instead of `color-yiq(#000)`, you'd write `color: color-yiq(#000);`.
 
 ### Highlights
@@ -110,7 +111,7 @@ New to Bootstrap 4 is the [Reboot]({{ site.baseurl }}/docs/{{ site.docs_version
 ### Forms
 
 - Moved element resets to the `_reboot.scss` file.
-- Renamed `.control-label` to `.form-control-label`.
+- Renamed `.control-label` to `.col-form-label`.
 - Renamed `.input-lg` and `.input-sm` to `.form-control-lg` and `.form-control-sm`, respectively.
 - Dropped `.form-group-*` classes for simplicity's sake. Use `.form-control-*` classes instead now.
 - Dropped `.help-block` and replaced it with `.form-text` for block-level help text. For inline help text and other flexible options, use utility classes like `.text-muted`.
@@ -119,7 +120,7 @@ New to Bootstrap 4 is the [Reboot]({{ site.baseurl }}/docs/{{ site.docs_version
 - Horizontal forms overhauled:
   - Dropped the `.form-horizontal` class requirement.
   - `.form-group` no longer applies styles from the `.row` via mixin, so `.row` is now required for horizontal grid layouts (e.g., `<div class="form-group row">`).
-  - Added new `.form-control-label` class to vertically center labels with `.form-control`s.
+  - Added new `.col-form-label` class to vertically center labels with `.form-control`s.
   - Added new `.form-row` for compact form layouts with the grid classes (swap your `.row` for a `.form-row` and go).
 - Added custom forms support (for checkboxes, radios, selects, and file inputs).
 - Replaced `.has-error`, `.has-warning`, and `.has-success` classes with HTML5 form validation via CSS's `:invalid` and `:valid` pseudo-classes.