Add .navbar-nav-scroll for vertical scrolling of navbar content (#32037)

Co-authored-by: XhmikosR <xhmikosr@gmail.com>

scss/_navbar.scss

@@ -148,6 +148,11 @@
   background-size: 100%;
 }
 
+.navbar-nav-scroll {
+  max-height: var(--bs-scroll-height, 75vh);
+  overflow-y: auto;
+}
+
 // Generate series of `.navbar-expand-*` responsive classes for configuring
 // where your navbar collapses.
 .navbar-expand {
@@ -174,6 +179,10 @@
           }
         }
 
+        .navbar-nav-scroll {
+          overflow: visible;
+        }
+
         .navbar-collapse {
           display: flex !important; // stylelint-disable-line declaration-no-important
         }

site/content/docs/5.0/components/navbar.md

@@ -31,6 +31,7 @@ Navbars come with built-in support for a handful of sub-components. Choose from
 - Flex and spacing utilities for any form controls and actions.
 - `.navbar-text` for adding vertically centered strings of text.
 - `.collapse.navbar-collapse` for grouping and hiding navbar contents by a parent breakpoint.
+- Add an optional `.navbar-scroll` to set a `max-height` and [scroll expanded navbar content](#scrolling).
 
 Here's an example of all the sub-components included in a responsive light-themed navbar that automatically collapses at the `lg` (large) breakpoint.
 
@@ -477,6 +478,53 @@ Also note that **`.sticky-top` uses `position: sticky`, which [isn't fully suppo
 </nav>
 {{< /example >}}
 
+## Scrolling
+
+Add `.navbar-nav-scroll` to a `.navbar-collapse` (or other navbar sub-component) to enable vertical scrolling within the toggleable contents of a collapsed navbar. By default, scrolling kicks in at `75vh` (or 75% of the viewport height), but you can override that with the local CSS custom property `--bs-navbar-height` or custom styles. At larger viewports when the navbar is expanded, content will appear as it does in a default navbar.
+
+Please note that this behavior comes with a potential drawback of `overflow`—when setting `overflow-y: auto` (required to scroll the content here), `overflow-x` is the equivalent of `auto`, which will crop some horizontal content.
+
+Here's an example navbar using `.navbar-nav-scroll` with `style="--bs-scroll-height: 100px;"`, with some extra margin utilities for optimum spacing.
+
+{{< example >}}
+<nav class="navbar navbar-expand-lg navbar-light bg-light">
+  <div class="container-fluid">
+    <a class="navbar-brand" href="#">Navbar scroll</a>
+    <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarScroll" aria-controls="navbarScroll" aria-expanded="false" aria-label="Toggle navigation">
+      <span class="navbar-toggler-icon"></span>
+    </button>
+    <div class="collapse navbar-collapse" id="navbarScroll">
+      <ul class="navbar-nav me-auto my-2 my-lg-0 navbar-nav-scroll" style="--bs-scroll-height: 100px;">
+        <li class="nav-item">
+          <a class="nav-link active" aria-current="page" href="#">Home</a>
+        </li>
+        <li class="nav-item">
+          <a class="nav-link" href="#">Link</a>
+        </li>
+        <li class="nav-item dropdown">
+          <a class="nav-link dropdown-toggle" href="#" id="navbarScrollingDropdown" role="button" data-bs-toggle="dropdown" aria-expanded="false">
+            Link
+          </a>
+          <ul class="dropdown-menu" aria-labelledby="navbarScrollingDropdown">
+            <li><a class="dropdown-item" href="#">Action</a></li>
+            <li><a class="dropdown-item" href="#">Another action</a></li>
+            <li><hr class="dropdown-divider"></li>
+            <li><a class="dropdown-item" href="#">Something else here</a></li>
+          </ul>
+        </li>
+        <li class="nav-item">
+          <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Link</a>
+        </li>
+      </ul>
+      <form class="d-flex">
+        <input class="form-control me-2" type="search" placeholder="Search" aria-label="Search">
+        <button class="btn btn-outline-success" type="submit">Search</button>
+      </form>
+    </div>
+  </div>
+</nav>
+{{< /example >}}
+
 ## Responsive behaviors
 
 Navbars can use `.navbar-toggler`, `.navbar-collapse`, and `.navbar-expand{-sm|-md|-lg|-xl|-xxl}` classes to determine when their content collapses behind a button. In combination with other utilities, you can easily choose when to show or hide particular elements.