feat: add dark/light classname (#729)

* feat: add dark classname

* add light class

Author: garrettbear

src/css/dark-theme-colors.css

@@ -1,7 +1,8 @@
 /**
  * Dark Theme Colors
 */
-[data-theme='dark'] {
+[data-theme='dark'],
+.dark {
   /* For default neutral backgrounds */
   --color-background-default: var(--brand-colors-grey-grey800);
   /* For secondary neutral backgrounds. */

src/css/light-theme-colors.css

@@ -2,7 +2,8 @@
  * Light Theme Colors
  */
 :root,
-[data-theme='light'] {
+[data-theme='light'],
+.light {
   /* For default neutral backgrounds */
   --color-background-default: var(--brand-colors-grey-grey000);
   /* For secondary neutral backgrounds. */