Responsive containers (follow-up to #29095) (#29118)

* Follow-up to #29095

This PR fixes the responsive containers that were added in #29095, originally stubbed out in #25631. Apologies to @browner12 for getting that wrong.

Fixes #25631.

* update navbar as well because we cannot reset all containers uniformly

* Update navbars example to include container-xl example to ensure containers match

* rewrite responsive containers docs, add table of max-widths

* Update container docs
- Move table up to the intro
- Remove the container example because it's actually hella confusing
- Update and link to grid example as a demo instead

6 files changed, 177 insertions, 39 deletions

diff --git a/scss/_grid.scss b/scss/_grid.scss
index 5b8b8cb23..d36ee75d8 100644
--- a/scss/_grid.scss
+++ b/scss/_grid.scss
@@ -21,9 +21,17 @@
     }
 
     @include media-breakpoint-up($breakpoint, $grid-breakpoints) {
-      .container-#{$breakpoint} {
+      %responsive-container-#{$breakpoint} {
         max-width: $container-max-width;
       }
+
+      @each $name, $width in $grid-breakpoints {
+        @if ($container-max-width > $width or $breakpoint == $name) {
+          .container#{breakpoint-infix($name, $grid-breakpoints)} {
+            @extend %responsive-container-#{$breakpoint};
+          }
+        }
+      }
     }
   }
 }
diff --git a/scss/_navbar.scss b/scss/_navbar.scss
index 64c15f534..f9e2b792a 100644
--- a/scss/_navbar.scss
+++ b/scss/_navbar.scss
@@ -25,12 +25,23 @@
 
   // Because flex properties aren't inherited, we need to redeclare these first
   // few properties so that content nested within behave properly.
-  > [class^="container"] {
+  %container-flex-properties {
     display: flex;
     flex-wrap: wrap;
     align-items: center;
     justify-content: space-between;
   }
+
+  .container,
+  .container-fluid {
+    @extend %container-flex-properties;
+  }
+
+  @each $breakpoint, $container-max-width in $container-max-widths {
+    > .container#{breakpoint-infix($breakpoint, $container-max-widths)} {
+      @extend %container-flex-properties;
+    }
+  }
 }
 
 
@@ -139,10 +150,21 @@
 
     &#{$infix} {
       @include media-breakpoint-down($breakpoint) {
-        > [class^="container"] {
+        %container-navbar-expand-#{$breakpoint} {
           padding-right: 0;
           padding-left: 0;
         }
+
+        > .container,
+        > .container-fluid {
+          @extend %container-navbar-expand-#{$breakpoint};
+        }
+
+        @each $size, $container-max-width in $container-max-widths {
+          > .container#{breakpoint-infix($size, $container-max-widths)} {
+            @extend %container-navbar-expand-#{$breakpoint};
+          }
+        }
       }
 
       @include media-breakpoint-up($next) {
@@ -163,10 +185,21 @@
         }
 
         // For nesting containers, have to redeclare for alignment purposes
-        > [class^="container"] {
+        %container-nesting-#{$breakpoint} {
           flex-wrap: nowrap;
         }
 
+        > .container,
+        > .container-fluid {
+          @extend %container-nesting-#{$breakpoint};
+        }
+
+        @each $size, $container-max-width in $container-max-widths {
+          > .container#{breakpoint-infix($size, $container-max-widths)} {
+            @extend %container-nesting-#{$breakpoint};
+          }
+        }
+
         .navbar-collapse {
           display: flex !important; // stylelint-disable-line declaration-no-important
 
diff --git a/site/content/docs/4.3/examples/grid/index.html b/site/content/docs/4.3/examples/grid/index.html
index 24289cea5..1440cb734 100644
--- a/site/content/docs/4.3/examples/grid/index.html
+++ b/site/content/docs/4.3/examples/grid/index.html
@@ -126,12 +126,14 @@ include_js: false
 
 </div>
 
-<div class="container">
-  <h2 class="mt-4">Responsive containers</h2>
+<div class="container" id="containers">
+  <h2 class="mt-4">Containers</h2>
   <p>Additional classes added in Bootstrap v4.4 allow containers that are 100% wide until a particular breakpoint.</p>
 </div>
 
+<div class="container themed-container">.container</div>
 <div class="container-sm themed-container">.container-sm</div>
 <div class="container-md themed-container">.container-md</div>
 <div class="container-lg themed-container">.container-lg</div>
 <div class="container-xl themed-container">.container-xl</div>
+<div class="container-fluid themed-container">.container-fluid</div>
diff --git a/site/content/docs/4.3/examples/navbars/index.html b/site/content/docs/4.3/examples/navbars/index.html
index bdb4aeb01..3ec8bb9c7 100644
--- a/site/content/docs/4.3/examples/navbars/index.html
+++ b/site/content/docs/4.3/examples/navbars/index.html
@@ -221,6 +221,44 @@ extra_css:
 </nav>
 
 <nav class="navbar navbar-expand-lg navbar-dark bg-dark">
+  <div class="container-xl">
+    <a class="navbar-brand" href="#">Container XL</a>
+    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarsExample07XL" aria-controls="navbarsExample07XL" aria-expanded="false" aria-label="Toggle navigation">
+      <span class="navbar-toggler-icon"></span>
+    </button>
+
+    <div class="collapse navbar-collapse" id="navbarsExample07XL">
+      <ul class="navbar-nav mr-auto">
+        <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">
+          <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
+        </li>
+        <li class="nav-item dropdown">
+          <a class="nav-link dropdown-toggle" href="#" id="dropdown07XL" data-toggle="dropdown" aria-expanded="false">Dropdown</a>
+          <div class="dropdown-menu" aria-labelledby="dropdown07XL">
+            <a class="dropdown-item" href="#">Action</a>
+            <a class="dropdown-item" href="#">Another action</a>
+            <a class="dropdown-item" href="#">Something else here</a>
+          </div>
+        </li>
+      </ul>
+      <form class="form-inline my-2 my-md-0">
+        <input class="form-control" type="text" placeholder="Search" aria-label="Search">
+      </form>
+    </div>
+  </div>
+</nav>
+
+<div class="container-xl mt-n2 mb-3">
+  Matching .container-xl...
+</div>
+
+<nav class="navbar navbar-expand-lg navbar-dark bg-dark">
   <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarsExample08" aria-controls="navbarsExample08" aria-expanded="false" aria-label="Toggle navigation">
     <span class="navbar-toggler-icon"></span>
   </button>
diff --git a/site/content/docs/4.3/layout/overview.md b/site/content/docs/4.3/layout/overview.md
index 79b799ca0..3ad386121 100644
--- a/site/content/docs/4.3/layout/overview.md
+++ b/site/content/docs/4.3/layout/overview.md
@@ -9,18 +9,100 @@ toc: true
 
 ## Containers
 
-Containers are the most basic layout element in Bootstrap and are **required when using our default grid system**. While containers *can* be nested, most layouts do not require a nested container.
+Containers are the most basic layout element in Bootstrap and are **required when using our default grid system**. Containers are used to contain, pad, and (sometimes) center the content within them. While containers *can* be nested, most layouts do not require a nested container.
+
+Bootstrap comes with three different containers:
+
+- `.container`, which sets a `max-width` at each responsive breakpoint
+- `.container-fluid`, which is `width: 100%` at all breakpoints
+- `.container-{breakpoint}`, which is `width: 100%` until the specified breakpoint
+
+The table below illustrates how each container's `max-width` compares to the original `.container` and `.container-fluid` across each breakpoint.
+
+See them in action and compare them in our [Grid example]({{< docsref "/examples/grid#containers" >}}).
+
+<table class="table text-left">
+  <thead>
+    <tr>
+      <th></th>
+      <th>
+        Extra small<br>
+        <span class="font-weight-normal">&lt;576px</span>
+      </th>
+      <th>
+        Small<br>
+        <span class="font-weight-normal">&ge;576px</span>
+      </th>
+      <th>
+        Medium<br>
+        <span class="font-weight-normal">&ge;768px</span>
+      </th>
+      <th>
+        Large<br>
+        <span class="font-weight-normal">&ge;992px</span>
+      </th>
+      <th>
+        Extra large<br>
+        <span class="font-weight-normal">&ge;1200px</span>
+      </th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td><code>.container</code></td>
+      <td class="text-muted">100%</td>
+      <td>540px</td>
+      <td>720px</td>
+      <td>960px</td>
+      <td>1140px</td>
+    </tr>
+    <tr>
+      <td><code>.container-sm</code></td>
+      <td class="text-muted">100%</td>
+      <td>540px</td>
+      <td>720px</td>
+      <td>960px</td>
+      <td>1140px</td>
+    </tr>
+    <tr>
+      <td><code>.container-md</code></td>
+      <td class="text-muted">100%</td>
+      <td class="text-muted">100%</td>
+      <td>720px</td>
+      <td>960px</td>
+      <td>1140px</td>
+    </tr>
+    <tr>
+      <td><code>.container-lg</code></td>
+      <td class="text-muted">100%</td>
+      <td class="text-muted">100%</td>
+      <td class="text-muted">100%</td>
+      <td>960px</td>
+      <td>1140px</td>
+    </tr>
+    <tr>
+      <td><code>.container-xl</code></td>
+      <td class="text-muted">100%</td>
+      <td class="text-muted">100%</td>
+      <td class="text-muted">100%</td>
+      <td class="text-muted">100%</td>
+      <td>1140px</td>
+    </tr>
+    <tr>
+      <td><code>.container-fluid</code></td>
+      <td class="text-muted">100%</td>
+      <td class="text-muted">100%</td>
+      <td class="text-muted">100%</td>
+      <td class="text-muted">100%</td>
+      <td class="text-muted">100%</td>
+    </tr>
+  </tbody>
+</table>
 
 ### All-in-one
 
 Our default `.container` class is a responsive, fixed-width container, meaning its `max-width` changes at each breakpoint.
 
-<div class="bd-example">
-  <div class="example-container-element col-6 p-3 mx-auto">
-    .container
-  </div>
-</div>
-
 {{< highlight html >}}
 <div class="container">
   <!-- Content here -->
@@ -31,12 +113,6 @@ Our default `.container` class is a responsive, fixed-width container, meaning i
 
 Use `.container-fluid` for a full width container, spanning the entire width of the viewport.
 
-<div class="bd-example">
-  <div class="example-container-element p-3">
-    .container-fluid
-  </div>
-</div>
-
 {{< highlight html >}}
 <div class="container-fluid">
   ...
@@ -45,16 +121,7 @@ Use `.container-fluid` for a full width container, spanning the entire width of
 
 ### Responsive
 
-Responsive containers are new in Bootstrap v4.4. They allow you to specify a class that is 100% wide until particular breakpoint is reached and a `max-width` is applied. For example, `.container-sm` is 100% wide to start until the `sm` breakpoint is reached, where it will remain through the higher breakpoints.
-
-<div class="bd-example">
-  <div class="example-container-element p-3 mb-3">
-    .container-sm (100% wide until breakpoint)
-  </div>
-  <div class="example-container-element col-6 p-3 mx-auto">
-    .container-sm (With max-width at breakpoint)
-  </div>
-</div>
+Responsive containers are new in Bootstrap v4.4. They allow you to specify a class that is 100% wide until the specified breakpoint is reached, after which we apply `max-width`s for each of the higher breakpoints. For example, `.container-sm` is 100% wide to start until the `sm` breakpoint is reached, where it will scale up with `md`, `lg`, and `xl`.
 
 {{< highlight html >}}
 <div class="container-sm">100% wide until small breakpoint</div>
diff --git a/site/static/docs/4.3/assets/scss/_component-examples.scss b/site/static/docs/4.3/assets/scss/_component-examples.scss
index 60f594232..1a3fa1d86 100644
--- a/site/static/docs/4.3/assets/scss/_component-examples.scss
+++ b/site/static/docs/4.3/assets/scss/_component-examples.scss
@@ -75,16 +75,6 @@
 
 
 //
-// Container illustrations
-//
-
-.example-container-element {
-  background-color: rgba($blue, .25);
-  border: 1px solid rgba($blue, .25);
-}
-
-
-//
 // Docs examples
 //