Update color mode mixin to support 'auto'

Author: BinaryMuse

src/support/mixins/color-modes.scss

@@ -1,14 +1,26 @@
 // Allows CSS to be scoped to a specific color mode
 @mixin color-mode($mode) {
   @if $mode == light {
-    :root,
+    :root:not(data-color-mode),
     [data-color-mode="light"] {
       @content;
     }
+
+    [data-color-mode="auto"] {
+      @media (prefers-color-scheme: light) {
+        @content;
+      }
+    }
   }
   @else if $mode == dark {
     [data-color-mode="dark"] {
       @content;
     }
+
+    [data-color-mode="auto"] {
+      @media (prefers-color-scheme: dark) {
+        @content;
+      }
+    }
   }
 }