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/content/docs/5.1/components/offcanvas.md

@@ -137,9 +137,54 @@ When backdrop is set to static, the offcanvas will not close when clicking outsi
 </div>
 {{< /example >}}
 
+## Responsive
+
+<small class="d-inline-flex px-2 py-1 fw-semibold text-success bg-success bg-opacity-10 rounded-2">Added in v5.2.0</small>
+
+Responsive offcanvas classes hide content outside the viewport from a specified breakpoint and down. Above that breakpoint, the contents within will behave as usual. For example, `.offcanvas-lg` hides content in an offcanvas below the `lg` breakpoint, but shows the content above the `lg` breakpoint.
+
+<div class="bd-example">
+  <button class="btn btn-primary d-lg-none" type="button" data-bs-toggle="offcanvas" data-bs-target="#offcanvasResponsive" aria-controls="offcanvasResponsive">Toggle offcanvas</button>
+
+  <div class="alert alert-info d-none d-lg-block">Resize your browser to show the responsive offcanvas toggle.</div>
+
+  <div class="offcanvas-lg offcanvas-end" tabindex="-1" id="offcanvasResponsive" aria-labelledby="offcanvasResponsiveLabel">
+    <div class="offcanvas-header">
+      <h5 class="offcanvas-title" id="offcanvasResponsiveLabel">Responsive offcanvas</h5>
+      <button type="button" class="btn-close" data-bs-dismiss="offcanvas" aria-label="Close"></button>
+    </div>
+    <div class="offcanvas-body">
+      <p class="mb-0">This is content within an <code>.offcanvas-lg</code>.</p>
+    </div>
+  </div>
+</div>
+
+```html
+<button class="btn btn-primary" type="button" data-bs-toggle="offcanvas" data-bs-target="#offcanvasResponsive" aria-controls="offcanvasResponsive">Toggle offcanvas</button>
+
+<div class="offcanvas-lg offcanvas-end" tabindex="-1" id="offcanvasResponsive" aria-labelledby="offcanvasResponsiveLabel">
+  <div class="offcanvas-header">
+    <h5 class="offcanvas-title" id="offcanvasResponsiveLabel">Responsive offcanvas</h5>
+    <button type="button" class="btn-close" data-bs-dismiss="offcanvas" aria-label="Close"></button>
+  </div>
+  <div class="offcanvas-body">
+    <p class="mb-0">This is content within an <code>.offcanvas-lg</code>.</p>
+  </div>
+</div>
+```
+
+Responsive offcanvas classes are available across for each breakpoint.
+
+- `.offcanvas`
+- `.offcanvas-sm`
+- `.offcanvas-md`
+- `.offcanvas-lg`
+- `.offcanvas-xl`
+- `.offcanvas-xxl`
+
 ## Placement
 
-There's no default placement for offcanvas components, so you must add one of the modifier classes below;
+There's no default placement for offcanvas components, so you must add one of the modifier classes below.
 
 - `.offcanvas-start` places offcanvas on the left of the viewport (shown above)
 - `.offcanvas-end` places offcanvas on the right of the viewport
@@ -194,10 +239,18 @@ Try the top, right, and bottom examples out below.
 
 Since the offcanvas panel is conceptually a modal dialog, be sure to add `aria-labelledby="..."`—referencing the offcanvas title—to `.offcanvas`. Note that you don’t need to add `role="dialog"` since we already add it via JavaScript.
 
-## Sass
+## CSS
 
 ### Variables
 
+<small class="d-inline-flex px-2 py-1 fw-semibold text-success bg-success bg-opacity-10 rounded-2">Added in v5.2.0</small>
+
+As part of Bootstrap's evolving CSS variables approach, offcanvas now uses local CSS variables on `.offcanvas` for enhanced real-time customization. Values for the CSS variables are set via Sass, so Sass customization is still supported, too.
+
+{{< scss-docs name="offcanvas-css-vars" file="scss/_offcanvas.scss" >}}
+
+### Sass variables
+
 {{< scss-docs name="offcanvas-variables" file="scss/_variables.scss" >}}
 
 ## Usage