build(deps): Bootstrap and Bootswatch 5.3.8

Bootstrap SCSS, the JS bundle and the Bootswatch themes go from 5.3.3 to
5.3.8 (bug fixes only), and wvc-main.min.css is recompiled from zephyr.
Bootswatch now gives table text the body color, and Lux drops card and
modal header borders.

Tests compile every theme with the pinned libsass and check that the
shipped CSS is zephyr from these sources. The update and rollback steps
put back the two files a theme change rewrites, or git refuses to pull
over them.

dev/scss/bootstrap/mixins/_banner.scss

@@ -1,7 +1,7 @@
 @mixin bsBanner($file) {
   /*!
-   * Bootstrap #{$file} v5.3.3 (https://getbootstrap.com/)
-   * Copyright 2011-2024 The Bootstrap Authors
+   * Bootstrap #{$file} v5.3.8 (https://getbootstrap.com/)
+   * Copyright 2011-2025 The Bootstrap Authors
    * Licensed under MIT (https://github.com/twbs/bootstrap/blob/main/LICENSE)
    */
 }

dev/scss/bootstrap/mixins/_box-shadow.scss

@@ -1,17 +1,23 @@
 @mixin box-shadow($shadow...) {
   @if $enable-shadows {
     $result: ();
+    $has-single-value: false;
+    $single-value: null;
 
     @each $value in $shadow {
       @if $value != null {
-        $result: append($result, $value, "comma");
-      }
-      @if $value == none and length($shadow) > 1 {
-        @warn "The keyword 'none' must be used as a single argument.";
+        @if $value == none or $value == initial or $value == inherit or $value == unset {
+          $has-single-value: true;
+          $single-value: $value;
+        } @else {
+          $result: append($result, $value, "comma");
+        }
       }
     }
 
-    @if (length($result) > 0) {
+    @if $has-single-value {
+      box-shadow: $single-value;
+    } @else if (length($result) > 0) {
       box-shadow: $result;
     }
   }

dev/scss/bootstrap/mixins/_grid.scss

@@ -72,7 +72,7 @@
     @include media-breakpoint-up($breakpoint, $breakpoints) {
       // Provide basic `.col-{bp}` classes for equal-width flexbox columns
       .col#{$infix} {
-        flex: 1 0 0%; // Flexbugs #4: https://github.com/philipwalton/flexbugs#flexbug-4
+        flex: 1 0 0;
       }
 
       .row-cols#{$infix}-auto > * {

dev/scss/bootstrap/mixins/_visually-hidden.scss

@@ -19,12 +19,17 @@
   &:not(caption) {
     position: absolute !important;
   }
+
+  // Fix to prevent overflowing children to become focusable
+  * {
+    overflow: hidden !important;
+  }
 }
 
 // Use to only display content when it's focused, or one of its child elements is focused
 // (i.e. when focus is within the element/container that the class was applied to)
 //
-// Useful for "Skip to main content" links; see https://www.w3.org/TR/2013/NOTE-WCAG20-TECHS-20130905/G1
+// Useful for "Skip to main content" links; see https://www.w3.org/WAI/WCAG22/Techniques/general/G1.html
 
 @mixin visually-hidden-focusable() {
   &:not(:focus):not(:focus-within) {