Allow `<mark>` colors customization for color modes (#39141)

scss/_reboot.scss

@@ -217,6 +217,7 @@ small {
 
 mark {
   padding: $mark-padding;
+  color: var(--#{$prefix}highlight-color);
   background-color: var(--#{$prefix}highlight-bg);
 }
 

scss/_root.scss

@@ -91,6 +91,7 @@
   }
 
   --#{$prefix}code-color: #{$code-color};
+  --#{$prefix}highlight-color: #{$mark-color};
   --#{$prefix}highlight-bg: #{$mark-bg};
 
   // scss-docs-start root-border-var
@@ -171,6 +172,8 @@
     --#{$prefix}link-hover-color-rgb: #{to-rgb($link-hover-color-dark)};
 
     --#{$prefix}code-color: #{$code-color-dark};
+    --#{$prefix}highlight-color: #{$mark-color-dark};
+    --#{$prefix}highlight-bg: #{$mark-bg-dark};
 
     --#{$prefix}border-color: #{$border-color-dark};
     --#{$prefix}border-color-translucent: #{$border-color-translucent-dark};

scss/_variables-dark.scss

@@ -53,6 +53,8 @@ $headings-color-dark:               inherit !default;
 $link-color-dark:                   tint-color($primary, 40%) !default;
 $link-hover-color-dark:             shift-color($link-color-dark, -$link-shade-percentage) !default;
 $code-color-dark:                   tint-color($code-color, 40%) !default;
+$mark-color-dark:                   $body-color-dark !default;
+$mark-bg-dark:                      $yellow-800 !default;
 
 
 //

scss/_variables.scss

@@ -718,6 +718,7 @@ $dt-font-weight:              $font-weight-bold !default;
 $list-inline-padding:         .5rem !default;
 
 $mark-padding:                .1875em !default;
+$mark-color:                  $body-color !default;
 $mark-bg:                     $yellow-100 !default;
 // scss-docs-end type-variables