From 9d87bd7a30c1874a9c3d60041a4042228753dd0e Mon Sep 17 00:00:00 2001
From: XhmikosR <xhmikosr@gmail.com>
Date: Tue, 19 Jan 2021 08:18:19 +0200
Subject: [PATCH] Backport #32037 (#32833)

* Backport #32037

Add `.navbar-nav-scroll` for vertical scrolling of navbar content

* drop the css var for a Sass css

Co-authored-by: Mark Otto <markdotto@gmail.com>
---
 scss/_navbar.scss                          |  9 +++++
 scss/_variables.scss                       |  2 +
 site/content/docs/4.5/components/navbar.md | 45 ++++++++++++++++++++++
 3 files changed, 56 insertions(+)

diff --git a/scss/_navbar.scss b/scss/_navbar.scss
index 5d4b6cd6b885..cf5b667908a2 100644
--- a/scss/_navbar.scss
+++ b/scss/_navbar.scss
@@ -139,6 +139,11 @@
   background: 50% / 100% 100% no-repeat;
 }
 
+.navbar-nav-scroll {
+  max-height: $navbar-nav-scroll-max-height;
+  overflow-y: auto;
+}
+
 // Generate series of `.navbar-expand-*` responsive classes for configuring
 // where your navbar collapses.
 .navbar-expand {
@@ -198,6 +203,10 @@
           }
         }
 
+        .navbar-nav-scroll {
+          overflow: visible;
+        }
+
         .navbar-collapse {
           display: flex !important; // stylelint-disable-line declaration-no-important
 
diff --git a/scss/_variables.scss b/scss/_variables.scss
index fc02b80e17ef..0a260b96fb6e 100644
--- a/scss/_variables.scss
+++ b/scss/_variables.scss
@@ -731,6 +731,8 @@ $navbar-toggler-padding-x:          .75rem !default;
 $navbar-toggler-font-size:          $font-size-lg !default;
 $navbar-toggler-border-radius:      $btn-border-radius !default;
 
+$navbar-nav-scroll-max-height:      75vh !default;
+
 $navbar-dark-color:                 rgba($white, .5) !default;
 $navbar-dark-hover-color:           rgba($white, .75) !default;
 $navbar-dark-active-color:          $white !default;
diff --git a/site/content/docs/4.5/components/navbar.md b/site/content/docs/4.5/components/navbar.md
index 07fff3b35f69..25c5718851ce 100644
--- a/site/content/docs/4.5/components/navbar.md
+++ b/site/content/docs/4.5/components/navbar.md
@@ -438,6 +438,51 @@ 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 inline 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="max-height: 100px;"`, with some extra margin utilities for optimum spacing.
+
+{{< example >}}
+<nav class="navbar navbar-expand-lg navbar-light bg-light">
+  <a class="navbar-brand" href="#">Navbar scroll</a>
+  <button class="navbar-toggler" type="button" data-toggle="collapse" data-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 mr-auto my-2 my-lg-0 navbar-nav-scroll" style="max-height: 100px;">
+      <li class="nav-item active">
+        <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></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-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 mr-2" type="search" placeholder="Search" aria-label="Search">
+      <button class="btn btn-outline-success" type="submit">Search</button>
+    </form>
+  </div>
+</nav>
+{{< /example >}}
+
 ## Responsive behaviors
 
 Navbars can use `.navbar-toggler`, `.navbar-collapse`, and `.navbar-expand{-sm|-md|-lg|-xl}` 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.