Add dark mode support (#35857)

* Add dark mode to docs

* Minor fix: missing space indentation

* Minor fix: revert utilities/z-index added-in modification

* Remove prev: and next: from doc because extracted to another PR

* Use .bg-body-tertiary in all Utilities > Overflow examples

* fix example

* Fix up spacing examples

* Update box-shadow Sass variables and utilities to auto-adjust to color modes

* Remove unused docs class

* Refactor form styles to use CSS variable for background images on .form-check and .form-switch

* Fix docs selector

* Rename shortcut for clarity

* Heading consistency

* Reintroduce missing 4th grid item in Utilities > Spacing example

* Fix bundlewatch

* .bd-callout* rendering is OK so removing comments in the code

* Update scss/_utilities.scss

Co-authored-by: Julien Déramond <julien.deramond@orange.com>

* Fix gutters example styling

* Fix text colors on background utils docs

* redesign and fix up position marker example, which doesn't show nicely in darkmode but at least isn't broken

* fix some color utils examples

* Deprecate mixin notice

* Deprecate notice for list-group-item-variant() mixin

* Revamp new link CSS vars

* Use map-keys in some each Sass files

* Remove list-group-item-variant mixin ref in sass loop desc

* Display CSS vars scoped to our built-in dark mode

* Revert previous commit

* Fix list group variant link

* Fix typo

* Remove imports of alert/list-group mixins in scss/_mixins.scss

* Small formatting + comments removal in scss/_content.scss

* Fix alert links colors

* fix dropdown border-radius mixin

* fix link color and underline again, this time using CSS var override for color var and fallback value for the underline

* fix colors on docs navbar for dark mode

* remove two changes

* missing ref

* another link underline fix, just use sass vars for link decoration for now

* missing color bg docs, plus move dropdown override to scss

* more changes from review

* fix some examples, drop unused docs navbar styles, update docs navbar color mode to use mixin

* Few fixes around type

- Restored CSS variable for color on headings, this time with a fallback value
- In conjunction, restored and wrapped the default CSS var with a null value check
- Split headings and paragraphs docs in Reboot, elaborated on them

* Restyle custom details > summary element in docs

* Rewrite some migration docs

* fix form checks

* Fix up some navbar styling, tweak docs callout

* Fix select images, mostly for validation styling

* Clean up some migration notes, document some new form control CSS vars, mention new variables-dark in sass docs

* Update site/content/docs/5.2/components/scrollspy.md

Co-authored-by: Julien Déramond <julien.deramond@orange.com>

* Apply suggestions from code review

Co-authored-by: Julien Déramond <julien.deramond@orange.com>

* mention form control css vars in migration guide

* Tweak grid and flex docs background examples

* clarify some docs

* fix some more things

Co-authored-by: Julien Déramond <juderamond@gmail.com>
Co-authored-by: Julien Déramond <julien.deramond@orange.com>

scss/_root.scss

@@ -1,4 +1,5 @@
-:root {
+:root,
+[data-bs-theme="light"] {
   // Note: Custom variable values only support SassScript inside `#{}`.
 
   // Colors
@@ -21,6 +22,18 @@
     --#{$prefix}#{$color}-rgb: #{$value};
   }
 
+  @each $color, $value in $theme-colors-text {
+    --#{$prefix}#{$color}-text: #{$value};
+  }
+
+  @each $color, $value in $theme-colors-bg-subtle {
+    --#{$prefix}#{$color}-bg-subtle: #{$value};
+  }
+
+  @each $color, $value in $theme-colors-border-subtle {
+    --#{$prefix}#{$color}-border-subtle: #{$value};
+  }
+
   --#{$prefix}white-rgb: #{to-rgb($white)};
   --#{$prefix}black-rgb: #{to-rgb($black)};
   --#{$prefix}body-color-rgb: #{to-rgb($body-color)};
@@ -44,12 +57,45 @@
   --#{$prefix}body-font-weight: #{$font-weight-base};
   --#{$prefix}body-line-height: #{$line-height-base};
   --#{$prefix}body-color: #{$body-color};
+
+  --#{$prefix}emphasis-color: #{$body-emphasis-color};
+  --#{$prefix}emphasis-color-rgb: #{to-rgb($body-emphasis-color)};
+
+  --#{$prefix}secondary-color: #{$body-secondary-color};
+  --#{$prefix}secondary-color-rgb: #{to-rgb($body-secondary-color)};
+  --#{$prefix}secondary-bg: #{$body-secondary-bg};
+  --#{$prefix}secondary-bg-rgb: #{to-rgb($body-secondary-bg)};
+
+  --#{$prefix}tertiary-color: #{$body-tertiary-color};
+  --#{$prefix}tertiary-color-rgb: #{to-rgb($body-tertiary-color)};
+  --#{$prefix}tertiary-bg: #{$body-tertiary-bg};
+  --#{$prefix}tertiary-bg-rgb: #{to-rgb($body-tertiary-bg)};
+
   @if $body-text-align != null {
     --#{$prefix}body-text-align: #{$body-text-align};
   }
   --#{$prefix}body-bg: #{$body-bg};
+  --#{$prefix}body-bg-rgb: #{to-rgb($body-bg)};
   // scss-docs-end root-body-variables
 
+  @if $headings-color != null {
+    --#{$prefix}heading-color: #{$headings-color};
+  }
+
+  --#{$prefix}link-color: #{$link-color};
+  --#{$prefix}link-color-rgb: #{to-rgb($link-color)};
+  --#{$prefix}link-decoration: #{$link-decoration};
+
+  --#{$prefix}link-hover-color: #{$link-hover-color};
+  --#{$prefix}link-hover-color-rgb: #{to-rgb($link-hover-color)};
+
+  @if $link-hover-decoration != null {
+    --#{$prefix}link-hover-decoration: #{$link-hover-decoration};
+  }
+
+  --#{$prefix}code-color: #{$code-color};
+  --#{$prefix}highlight-bg: #{$mark-bg};
+
   // scss-docs-start root-border-var
   --#{$prefix}border-width: #{$border-width};
   --#{$prefix}border-style: #{$border-style};
@@ -64,10 +110,17 @@
   --#{$prefix}border-radius-pill: #{$border-radius-pill};
   // scss-docs-end root-border-var
 
-  --#{$prefix}link-color: #{$link-color};
-  --#{$prefix}link-hover-color: #{$link-hover-color};
+  --#{$prefix}box-shadow: #{$box-shadow};
+  --#{$prefix}box-shadow-sm: #{$box-shadow-sm};
+  --#{$prefix}box-shadow-lg: #{$box-shadow-lg};
+  --#{$prefix}box-shadow-inset: #{$box-shadow-inset};
 
-  --#{$prefix}code-color: #{$code-color};
+  --#{$prefix}emphasis-color: #{$emphasis-color};
+
+  // scss-docs-start form-control-vars
+  --#{$prefix}form-control-bg: var(--#{$prefix}body-bg);
+  --#{$prefix}form-control-disabled-bg: var(--#{$prefix}secondary-bg);
+  // scss-docs-end form-control-vars
 
   --#{$prefix}highlight-bg: #{$mark-bg};
 
@@ -75,3 +128,68 @@
     --#{$prefix}breakpoint-#{$name}: #{$value};
   }
 }
+
+@if $enable-dark-mode {
+  @include color-mode(dark) {
+    // scss-docs-start root-dark-mode-vars
+    --#{$prefix}body-color: #{$body-color-dark};
+    --#{$prefix}body-color-rgb: #{to-rgb($body-color-dark)};
+    --#{$prefix}body-bg: #{$body-bg-dark};
+    --#{$prefix}body-bg-rgb: #{to-rgb($body-bg-dark)};
+
+    --#{$prefix}emphasis-color: #{$body-emphasis-color-dark};
+    --#{$prefix}emphasis-color-rgb: #{to-rgb($body-emphasis-color-dark)};
+
+    --#{$prefix}secondary-color: #{$body-secondary-color-dark};
+    --#{$prefix}secondary-color-rgb: #{to-rgb($body-secondary-color-dark)};
+    --#{$prefix}secondary-bg: #{$body-secondary-bg-dark};
+    --#{$prefix}secondary-bg-rgb: #{to-rgb($body-secondary-bg-dark)};
+
+    --#{$prefix}tertiary-color: #{$body-tertiary-color-dark};
+    --#{$prefix}tertiary-color-rgb: #{to-rgb($body-tertiary-color-dark)};
+    --#{$prefix}tertiary-bg: #{$body-tertiary-bg-dark};
+    --#{$prefix}tertiary-bg-rgb: #{to-rgb($body-tertiary-bg-dark)};
+
+    --#{$prefix}emphasis-color: #{$emphasis-color-dark};
+
+    --#{$prefix}primary-text: #{$primary-text-dark};
+    --#{$prefix}secondary-text: #{$secondary-text-dark};
+    --#{$prefix}success-text: #{$success-text-dark};
+    --#{$prefix}info-text: #{$info-text-dark};
+    --#{$prefix}warning-text: #{$warning-text-dark};
+    --#{$prefix}danger-text: #{$danger-text-dark};
+    --#{$prefix}light-text: #{$light-text-dark};
+    --#{$prefix}dark-text: #{$dark-text-dark};
+
+    --#{$prefix}primary-bg-subtle: #{$primary-bg-subtle-dark};
+    --#{$prefix}secondary-bg-subtle: #{$secondary-bg-subtle-dark};
+    --#{$prefix}success-bg-subtle: #{$success-bg-subtle-dark};
+    --#{$prefix}info-bg-subtle: #{$info-bg-subtle-dark};
+    --#{$prefix}warning-bg-subtle: #{$warning-bg-subtle-dark};
+    --#{$prefix}danger-bg-subtle: #{$danger-bg-subtle-dark};
+    --#{$prefix}light-bg-subtle: #{$light-bg-subtle-dark};
+    --#{$prefix}dark-bg-subtle: #{$dark-bg-subtle-dark};
+
+    --#{$prefix}primary-border-subtle: #{$primary-border-subtle-dark};
+    --#{$prefix}secondary-border-subtle: #{$secondary-border-subtle-dark};
+    --#{$prefix}success-border-subtle: #{$success-border-subtle-dark};
+    --#{$prefix}info-border-subtle: #{$info-border-subtle-dark};
+    --#{$prefix}warning-border-subtle: #{$warning-border-subtle-dark};
+    --#{$prefix}danger-border-subtle: #{$danger-border-subtle-dark};
+    --#{$prefix}light-border-subtle: #{$light-border-subtle-dark};
+    --#{$prefix}dark-border-subtle: #{$dark-border-subtle-dark};
+
+    --#{$prefix}heading-color: #{$headings-color-dark};
+
+    --#{$prefix}link-color: #{$link-color-dark};
+    --#{$prefix}link-hover-color: #{$link-hover-color-dark};
+    --#{$prefix}link-color-rgb: #{to-rgb($link-color-dark)};
+    --#{$prefix}link-hover-color-rgb: #{to-rgb($link-hover-color-dark)};
+
+    --#{$prefix}code-color: #{$code-color-dark};
+
+    --#{$prefix}border-color: #{$border-color-dark};
+    --#{$prefix}border-color-translucent: #{$border-color-translucent-dark};
+    // scss-docs-end root-dark-mode-vars
+  }
+}