Add color-scheme mixin

scss/mixins/_color-scheme.scss

@@ -0,0 +1,17 @@
+// scss-docs-start mixin-color-scheme
+@mixin color-scheme($name) {
+  @if $name == dark {
+    @media (prefers-color-scheme: dark) {
+      @content;
+    }
+  } @else if $name == light {
+    @media (prefers-color-scheme: light) {
+      @content;
+    }
+  } @else {
+    @media (prefers-color-scheme: #{$name}) {
+      @content;
+    }
+  }
+}
+// scss-docs-end mixin-color-scheme