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/base/_images.css

@@ -3,7 +3,7 @@
 figure,
 img {
   &.image {
-    --image-padding: .75rem;
+    --image-padding: 0.75rem;
 
     @media (min-width: 666px) {
       &.center {