Colorize API stabilitity index headers in docs

Noted in @shtylman's #3898, API stability notes are easy to overlook
in the html documentation. This can be especially troublesome if the API
is deprecated. This commit gives visual feedback by adding in a class
to the html docs when they're generated. The API headers with
corresponding colors are also listed in the 'About this Documentation'
page for easy reference.

1 files changed, 24 insertions, 0 deletions

diff --git a/doc/api_assets/style.css b/doc/api_assets/style.css
index 5523984ce15..de3f07c58c5 100644
--- a/doc/api_assets/style.css
+++ b/doc/api_assets/style.css
@@ -67,6 +67,30 @@ code a:hover {
   margin: 0;
 }
 
+.api_stability_0 {
+  border-color: #D60027;
+}
+
+.api_stability_1 {
+  border-color: #EC5315;
+}
+
+.api_stability_2 {
+  border-color: #FFD700;
+}
+
+.api_stability_3 {
+  border-color: #AEC516;
+}
+
+.api_stability_4 {
+  border-color: #009431;
+}
+
+.api_stability_5 {
+  border-color: #0084B6;
+}
+
 ul.plain {
   list-style: none;
 }