Placeholder for transitions reset to prevent code duplication… (#29870)

Co-authored-by: Martijn Cuppens <martijn.cuppens@gmail.com>
Co-authored-by: XhmikosR <xhmikosr@gmail.com>

scss/_reboot.scss

@@ -583,3 +583,14 @@ main {
 [hidden] {
   display: none !important;
 }
+
+// Placeholder used to reset transitions, when user prefers reduced motion
+
+@if $enable-prefers-reduced-motion-media-query {
+  @media (prefers-reduced-motion: reduce) {
+    %no-transition {
+      // stylelint-disable-next-line property-blacklist
+      transition: none !important;
+    }
+  }
+}

scss/_variables.scss

@@ -212,6 +212,14 @@ $escaped-characters: (
   (")","%29"),
 ) !default;
 
+// Selectors which are isolated in the transition mixin to prevent invalid selector stack
+$pseudo-vendor-prefixes: (
+  "::-webkit-",
+  "::-moz-",
+  "::-ms-"
+) !default;
+
+
 // Options
 //
 // Quickly modify global styling by enabling or disabling optional features.

scss/mixins/_transition.scss

@@ -9,8 +9,19 @@
   }
 
   @if $enable-prefers-reduced-motion-media-query {
-    @media (prefers-reduced-motion: reduce) {
+    $isolate: false;
-      transition: none;
+    @each $selector in $pseudo-vendor-prefixes {
+      @if str-index(quote(#{&}), $selector) {
+        $isolate: true;
+      }
+    }
+
+    @if $isolate {
+      @media (prefers-reduced-motion: reduce) {
+        transition: none;
+      }
+    } @else {
+      @extend %no-transition;
     }
   }
 }

site/assets/scss/docs.scss

@@ -51,3 +51,12 @@
 @import "syntax";
 @import "anchor";
 @import "algolia";
+
+@if $enable-prefers-reduced-motion-media-query {
+  @media (prefers-reduced-motion: reduce) {
+    %no-transition {
+      // stylelint-disable-next-line property-blacklist, declaration-no-important
+      transition: none !important;
+    }
+  }
+}

site/content/docs/4.3/migration.md

@@ -41,6 +41,7 @@ Changes to our source Sass files and compiled CSS.
 - Line heights are dropped from several components to simplify our codebase. The `button-size()` and `pagination-size()` do not accept line height parameters anymore. [See #29271](https://github.com/twbs/bootstrap/pull/29271)
 - The `button-variant()` mixin now accepts 3 optional color parameters, for each button state, to override the color provided by `color-yiq()`. By default, these parameters will find which color provides more contrast against the button state's background color with `color-yiq()`.
 - The `button-outline-variant()` mixin now accepts an additional argument, `$active-color`, for setting the button's active state text color. By default, this parameter will find which color provides more contrast against the button's active background color with `color-yiq()`.
+- The `transition()` mixin now extends `%no-transition` placeholder to handle `prefers-reduced-motion` media query-except vendor prefixes listed in new `$pseudo-vendor-prefixes` variable. [See #29870](https://github.com/twbs/bootstrap/pull/29870/)
 
 ## JavaScript