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/_content.scss

@@ -2,14 +2,13 @@
 // Bootstrap docs content theming
 //
 
-// Offset for the sticky header
-@include media-breakpoint-up(md) {
-  :root {
-    scroll-padding-top: 4rem;
-  }
-}
-
 .bd-content {
+  // Offset content from fixed navbar when jumping to headings
+  > :target {
+    padding-top: 5rem;
+    margin-top: -5rem;
+  }
+
   > h2:not(:first-child) {
     margin-top: 3rem;
   }
@@ -46,6 +45,10 @@
       border-bottom: 2px solid currentcolor;
     }
 
+    tbody:not(:first-child) {
+      border-top: 2px solid currentcolor;
+    }
+
     th,
     td {
       &:first-child {
@@ -59,12 +62,24 @@
 
     // Prevent breaking of code
     // stylelint-disable-next-line selector-max-compound-selectors
+    th,
     td:first-child > code {
       white-space: nowrap;
     }
   }
 }
 
+.table-options {
+  td:nth-child(2) {
+    min-width: 160px;
+  }
+}
+
+.table-options td:last-child,
+.table-utilities td:last-child {
+  min-width: 280px;
+}
+
 .bd-title {
   @include font-size(3rem);
 }
@@ -77,3 +92,35 @@
 .bd-bg-violet {
   background-color: $bd-violet;
 }
+
+.bi {
+  width: 1em;
+  height: 1em;
+  fill: currentcolor;
+}
+
+.icon-link {
+  display: flex;
+  align-items: center;
+  text-decoration-color: rgba($primary, .5);
+  text-underline-offset: .5rem;
+  backface-visibility: hidden;
+
+  .bi {
+    width: 1.5em;
+    height: 1.5em;
+    transition: .2s ease-in-out transform; // stylelint-disable-line property-disallowed-list
+  }
+
+  &:hover {
+    .bi {
+      transform: translate3d(5px, 0, 0);
+    }
+  }
+}
+
+.border-lg-start {
+  @include media-breakpoint-up(lg) {
+    border-left: $border-width solid $border-color;
+  }
+}