Remove unused CSS. (#24872)

assets/scss/_featured-sites.scss

-.bd-featured-sites {
-  margin-right: -1px;
-  margin-left: -1px;
-}
-.bd-featured-sites .col-6 {
-  padding: 1px;
-}
-.bd-featured-sites .img-fluid {
-  margin-top: 0;
-}
-
-@media (min-width: 768px) {
-  .bd-featured-sites .col-sm-3:first-child img {
-    border-top-left-radius: .25rem;
-    border-bottom-left-radius: .25rem;
-  }
-  .bd-featured-sites .col-sm-3:last-child img {
-    border-top-right-radius: .25rem;
-    border-bottom-right-radius: .25rem;
-  }
-}

assets/scss/_masthead.scss

@@ -41,11 +41,6 @@
   }
 }
 
-.bd-pretext {
-  overflow: hidden;
-  resize: none;
-}
-
 .half-rule {
   width: 6rem;
   margin: 2.5rem 0;

assets/scss/_page-header.scss

-// stylelint-disable declaration-no-important
-
-.bd-pageheader {
-  padding: 2rem ($grid-gutter-width / 2);
-  margin-bottom: 1.5rem;
-  color: $bd-purple-light;
-  text-align: center;
-  background-color: $bd-purple;
-
-  .container {
-    position: relative;
-  }
-
-  h1 {
-    font-size: 3rem;
-    font-weight: 400;
-    color: #fff;
-  }
-
-  p {
-    margin-bottom: 0;
-    font-size: 1.25rem;
-    font-weight: 300;
-  }
-
-  @include media-breakpoint-up(sm) {
-    padding-top: 4rem;
-    padding-bottom: 4rem;
-    margin-bottom: 3rem;
-    text-align: left;
-
-    .carbonad {
-      margin: 2rem 0 0 !important;
-    }
-  }
-
-  @include media-breakpoint-up(md) {
-    h1 {
-      font-size: 4rem;
-    }
-
-    p {
-      font-size: 1.5rem;
-    }
-  }
-
-  @include media-breakpoint-up(lg) {
-    h1,
-    p {
-      margin-right: 380px;
-    }
-
-    .carbonad {
-      position: absolute;
-      top: 0;
-      right: .75rem; // offset from the .container's padding
-      margin: 0 !important;
-    }
-  }
-}

assets/scss/_responsive-tests.scss

-//
-// Responsive tests
-//
-
-// Responsive (scrollable) doc tables
-.table-responsive .highlight pre {
-  white-space: normal;
-}
-
-// Utility classes table
-.bd-table th small {
-  display: block;
-  font-weight: 400;
-  color: #999;
-}

assets/scss/docs.scss

@@ -32,15 +32,12 @@
 @import "variables";
 @import "nav";
 @import "masthead";
-@import "featured-sites";
 @import "ads";
 @import "content";
-@import "page-header";
 @import "skiplink";
 @import "sidebar";
 @import "footer";
 @import "component-examples";
-@import "responsive-tests";
 @import "buttons";
 @import "callouts";
 @import "examples";