Convert alerts to CSS variables (#35401)

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

.bundlewatch.config.json

@@ -26,11 +26,11 @@
     },
     {
       "path": "./dist/css/bootstrap.css",
-      "maxSize": "25.5 kB"
+      "maxSize": "26 kB"
     },
     {
       "path": "./dist/css/bootstrap.min.css",
-      "maxSize": "23.25 kB"
+      "maxSize": "23.5 kB"
     },
     {
       "path": "./dist/js/bootstrap.bundle.js",

scss/_alert.scss

@@ -3,11 +3,22 @@
 //
 
 .alert {
+  // scss-docs-start alert-css-vars
+  --#{$variable-prefix}alert-bg: transparent;
+  --#{$variable-prefix}alert-padding: #{$alert-padding-y $alert-padding-x};
+  --#{$variable-prefix}alert-margin-bottom: #{$alert-margin-bottom};
+  --#{$variable-prefix}alert-color: #{$alert-padding-y $alert-padding-x};
+  --#{$variable-prefix}alert-border-color: transparent;
+  --#{$variable-prefix}alert-border: #{$alert-border-width} solid var(--#{$variable-prefix}alert-border-color);
+  --#{$variable-prefix}alert-border-radius: #{$alert-border-radius};
+  // scss-docs-end alert-css-vars
+
   position: relative;
-  padding: $alert-padding-y $alert-padding-x;
-  margin-bottom: $alert-margin-bottom;
-  border: $alert-border-width solid transparent;
-  @include border-radius($alert-border-radius);
+  padding: var(--#{$variable-prefix}alert-padding);
+  margin-bottom: var(--#{$variable-prefix}alert-margin-bottom);
+  background-color: var(--#{$variable-prefix}alert-bg);
+  border: var(--#{$variable-prefix}alert-border);
+  border-radius: var(--#{$variable-prefix}alert-border-radius, 0); // stylelint-disable-line property-disallowed-list
 }
 
 // Headings for larger alerts
@@ -47,6 +58,7 @@
   $alert-background: shift-color($value, $alert-bg-scale);
   $alert-border: shift-color($value, $alert-border-scale);
   $alert-color: shift-color($value, $alert-color-scale);
+
   @if (contrast-ratio($alert-background, $alert-color) < $min-contrast-ratio) {
     $alert-color: mix($value, color-contrast($alert-background), abs($alert-color-scale));
   }

scss/mixins/_alert.scss

@@ -1,8 +1,12 @@
 // scss-docs-start alert-variant-mixin
 @mixin alert-variant($background, $border, $color) {
-  color: $color;
-  @include gradient-bg($background);
-  border-color: $border;
+  --#{$variable-prefix}alert-color: #{$color};
+  --#{$variable-prefix}alert-bg: #{$background};
+  --#{$variable-prefix}alert-border-color: #{$border};
+
+  @if $enable-gradients {
+    background-image: var(--#{$variable-prefix}gradient);
+  }
 
   .alert-link {
     color: shade-color($color, 20%);

site/content/docs/5.1/components/alerts.md

@@ -156,19 +156,27 @@ You can see this in action with a live demo:
 When an alert is dismissed, the element is completely removed from the page structure. If a keyboard user dismisses the alert using the close button, their focus will suddenly be lost and, depending on the browser, reset to the start of the page/document. For this reason, we recommend including additional JavaScript that listens for the `closed.bs.alert` event and programmatically sets `focus()` to the most appropriate location in the page. If you're planning to move focus to a non-interactive element that normally does not receive focus, make sure to add `tabindex="-1"` to the element.
 {{< /callout >}}
 
-## Sass
+## CSS
 
 ### Variables
 
+<small class="d-inline-flex px-2 py-1 font-monospace text-muted border rounded-3">Added in v5.2.0</small>
+
+As part of Bootstrap's evolving CSS variables approach, buttons now use local CSS variables on `.alert` for enhanced real-time customization. Values for the CSS variables are set via Sass, so Sass customization is still supported, too.
+
+{{< scss-docs name="alert-css-vars" file="scss/_alert.scss" >}}
+
+### Sass variables
+
 {{< scss-docs name="alert-variables" file="scss/_variables.scss" >}}
 
-### Variant mixin
+### Sass mixin
 
 Used in combination with `$theme-colors` to create contextual modifier classes for our alerts.
 
 {{< scss-docs name="alert-variant-mixin" file="scss/mixins/_alert.scss" >}}
 
-### Loop
+### Sass loop
 
 Loop that generates the modifier classes with the `alert-variant()` mixin.