v5.2.0 design refresh, plus responsive offcanvas classes (#35736)

* Add responsive offcanvas classes

- Updates navbar-expand classes to de-dupe some styles—these shouldn't interfere now.
- Adds some JS to the offcanvas component to help with responsiveness

Co-Authored-By: GeoSot <geo.sotis@gmail.com>

* Redesign homepage, docs, and examples

Homepage:

- New Bootstrap purple navbar
- Redesigned masthead
- Rewrote and redesigned homepage content
- Replace Copy text with icons like Bootstrap Icons site across all ClipboardJS instances
- Fixed padding issues in site footer
- Match homepage button styles to examples page, use gap instead of tons of responsive margin utils

Docs:

- New navbar, no more subnav. Migrated search and version picker into the main navbar and refreshed the design of it all, including the responsive toggles.
- New sidebar navigation is always expanded, and now features Bootstrap Icons alongside section headings
- Sidebar navigation autoscrolls to active link for better usability
- Subnav and navbar padding issues ironed out
- Enhanced the version picker in anticipation of v5.2: we can now link right to the same page in the previous version.
- Redesign callouts to add more color to our pages
- Collapse table of contents on mobile
- Cleanup and redesign button styles with CSS variables
- Update design for subnav version dropdown
- Update highlight and example to be full-width until md
- Improve the Added In badges
- Turn the ToC into a well on mobile
- Redesign code snippets to better house two action buttons

Examples:

- Redesign Examples page layout
- Add new example for responsive offcanvases in navbars

* Convert offcanvas to CSS vars

* Feat: add resize handler to Offcanvas.js.

If we could use as default the `.offcanvas` class without modifiers, we then, could add a simplified selector
The selector itself, ignores the .offcanvas class as it doesn't have any responsive behavior
The `aria-modal` addon is to protect us, selection backdrop elements

* Separate examples code, Add some selectors, fix stackblitz btn

Co-authored-by: GeoSot <geo.sotis@gmail.com>

site/assets/scss/_component-examples.scss

@@ -85,21 +85,17 @@
 .bd-example {
   position: relative;
   padding: 1rem;
-  margin: 1rem ($bd-gutter-x * -1) 0;
-  border: solid $gray-300;
+  margin: 1rem ($bd-gutter-x * -.5) 0;
+  border: solid $border-color;
   border-width: 1px 0 0;
   @include clearfix();
 
-  @include media-breakpoint-up(sm) {
+  @include media-breakpoint-up(md) {
     padding: 1.5rem;
     margin-right: 0;
     margin-left: 0;
     border-width: 1px;
-    @include border-top-radius(.25rem);
-
-    + .bd-clipboard + .highlight {
-      @include border-bottom-radius(.25rem);
-    }
+    @include border-top-radius(var(--bs-border-radius));
   }
 
   + p {
@@ -348,12 +344,14 @@
 //
 
 .highlight {
-  padding: var(--bs-gutter-x) $bd-gutter-x;
+  position: relative;
+  padding: .75rem ($bd-gutter-x * .5);
   margin-bottom: 1rem;
   background-color: var(--bs-gray-100);
 
-  @include media-breakpoint-up(sm) {
-    padding: 1rem 1.5rem;
+  @include media-breakpoint-up(md) {
+    padding: .75rem 1.25rem;
+    @include border-radius(var(--bs-border-radius));
   }
 
   pre {
@@ -363,6 +361,11 @@
     white-space: pre;
     background-color: transparent;
     border: 0;
+
+    // Undo tabindex that's automatically added by Hugo
+    &:focus {
+      outline: 0;
+    }
   }
 
   pre code {
@@ -372,11 +375,22 @@
   }
 }
 
-.bd-content .highlight {
-  margin-right: $bd-gutter-x * -1;
-  margin-left: $bd-gutter-x * -1;
+.bd-example-snippet {
+  .highlight {
+    @include border-top-radius(0);
+    border: 1px solid $border-color;
+  }
+  .highlight-toolbar {
+    border: solid $border-color;
+    border-width: 0 1px;
+  }
+}
 
-  @include media-breakpoint-up(sm) {
+.bd-content .highlight {
+  margin-right: $bd-gutter-x * -.5;
+  margin-left: $bd-gutter-x * -.5;
+
+  @include media-breakpoint-up(md) {
     margin-right: 0;
     margin-left: 0;
   }