Clean: SASS - Dark mixin

src/contents/_activity_stream.scss

@@ -81,7 +81,7 @@
       --newtab-element-hover-color: color-mix(in srgb, currentColor 9%, transparent) !important;
     }
 
-    @media (-moz-toolbar-prefers-color-scheme: dark), (prefers-color-scheme: dark) {
+    @include Dark {
       #root {
         /* Default Dark Mode */
         --newtab-search-background-color: rgba(66, 65, 77, 1); /* Same as dark theme's --panel-background */

src/contents/_video_player.scss

@@ -17,7 +17,7 @@
     --media-background: linear-gradient(transparent, rgba(26,26,26,.85));
   }
 
-  @media (-moz-toolbar-prefers-color-scheme: dark), (prefers-color-scheme: dark) {
+  @include Dark {
     audio {
       --box-shadow1: rgba(249, 249, 250, 0.12);
       --box-shadow2: rgba(91, 91, 102, 0.12);

src/contents/proton_contents/_view_source.scss

@@ -7,7 +7,7 @@
     --view-source-green: var(--green-80);
     --view-source-purple: #800080; /* Like alphenglow */
   }
-  @media (-moz-toolbar-prefers-color-scheme: dark), (prefers-color-scheme: dark) {
+  @include Dark {
     :root {
       --view-source-green: var(--green-60);
       --view-source-purple: #c68aff;

src/theme/_proton_color.scss

@@ -108,7 +108,7 @@
   --card-shadow-hover: var(--card-shadow), 0 0 0 5px var(--card-outline-color);
 }
 
-@media (-moz-toolbar-prefers-color-scheme: dark), (prefers-color-scheme: dark) {
+@include Dark {
   :host,
   :root {
     /* Keep these in sync with layout/base/PresShell.cpp, and plaintext.css */

src/theme/system_default_theme/_win10.scss

@@ -274,7 +274,7 @@
     /* Light Theme */
     --lwt-accent-color: var(--win-bgcolor) !important;
   }
-  @media (-moz-toolbar-prefers-color-scheme: dark), (prefers-color-scheme: dark) {
+  @include Dark {
     :root[lwt-default-theme-in-dark-mode][lwthemetextcolor="bright"] {
       --toolbar-bgcolor: var(--win-component-bgcolor) !important; /* Original: rgba(43, 42, 51, 1) */
     }