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/layouts/_default/single.html

@@ -1,14 +1,19 @@
 {{ define "main" }}
   <header class="py-5 border-bottom">
-    <div class="container pt-md-1 pb-md-4">
+  <div class="container-xxl bd-gutter pt-md-1 pb-md-4">
       <div class="row">
         <div class="col-xl-8">
           <h1 class="bd-title mt-0">{{ .Title | markdownify }}</h1>
           <p class="bd-lead">{{ .Page.Params.Description | markdownify }}</p>
           {{ if eq .Title "Examples" }}
-          <div class="d-flex flex-column flex-sm-row">
-            <a href="{{ .Site.Params.download.dist_examples }}" class="btn btn-lg btn-bd-primary" onclick="ga('send', 'event', 'Examples', 'Hero', 'Download Examples');">Download examples</a>
-            <a href="{{ .Site.Params.download.source }}" class="btn btn-lg btn-outline-secondary mt-3 mt-sm-0 ms-sm-3" onclick="ga('send', 'event', 'Examples', 'Hero', 'Download');">Download source code</a>
+          <div class="d-flex flex-column flex-md-row gap-3">
+            <a href="{{ .Site.Params.download.dist_examples }}" class="btn btn-lg bd-btn-lg btn-bd-primary d-flex align-items-center justify-content-center fw-semibold" onclick="ga('send', 'event', 'Examples', 'Hero', 'Download Examples');">
+              <svg class="bi me-2" aria-hidden="true"><use xlink:href="#box-seam"></use></svg>
+              Download examples
+            </a>
+            <a href="{{ .Site.Params.download.source }}" class="btn btn-lg bd-btn-lg btn-outline-secondary" onclick="ga('send', 'event', 'Examples', 'Hero', 'Download');">
+              Download source code
+            </a>
           </div>
           {{ end }}
         </div>
@@ -20,7 +25,7 @@
   </header>
 
   <main class="bd-content order-1 py-5" id="content">
-    <div class="container">
+    <div class="container-xxl bd-gutter">
       {{ .Content }}
 
       {{ if eq .Title "Examples" }}
@@ -30,7 +35,7 @@
             <div class="masthead-followup-icon d-inline-block mb-2 text-white bg-danger">
               {{ partial "icons/droplet-fill.svg" (dict "width" "32" "height" "32") }}
             </div>
-              <h2 class="display-6 fw-normal">Go further with Bootstrap Themes</h2>
+            <h2 class="display-6 fw-normal">Go further with Bootstrap Themes</h2>
             <p class="col-md-10 col-lg-8 mx-auto lead">
               Need something more than these examples? Take Bootstrap to the next level with premium themes from the <a href="{{ .Site.Params.themes }}">official Bootstrap Themes marketplace</a>. They’re built as their own extended frameworks, rich with new components and plugins, documentation, and powerful build tools.
             </p>