Using color-scheme and light-dark() to implement dark mode (#154)

* Lint fixes.

* Implement light-dark().

* Lint css with biome, remove stylelint.

* Biome lint fixes.

* Dark mode adjustments.

* Style bug fixes.

* Colour adjustments.

* Move header and footer styles to base.

* Site header adjustments.

* Removing jQuery and umbrella libs. They where great but not needed anymore.

* Add colorScheme to optionally lock light/dark.

* Update README.

* Biome adjustments.

assets/css/components/_disabled.css

@@ -1,13 +1,13 @@
 .disabled {
   /* Re-set default cursor for disabled elements. */
   cursor: default;
-  color: var(--color-button-disabled);
+  color: var(--color-disabled);
 
   &:hover,
   &:focus,
   &:active {
     /* Override any link underlines and color changes. */
-    color: var(--color-button-disabled);
+    color: var(--color-disabled);
     text-decoration: none;
   }
 }