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.

layouts/_partials/mobilemenu.html

@@ -8,7 +8,7 @@
       <rect width="80" height="12" x="10" y="70" rx="5"></rect>
     </svg>
   </button>
-  <div class="mobile-nav__sheet link-inverted link-nav" id="sheet" aria-hidden="true">
+  <div class="mobile-nav__sheet link-nav" id="sheet" data-theme="dark" aria-hidden="true">
     <div class="mobile-nav__region">{{ if hugo.IsMultilingual }}{{ partial "language-selector.html" . }}{{ end }}</div>
     <nav class="mobile-nav__main-menu" aria-label="{{ i18n "menu_title" }}">
     <ul class="mobile-nav__navbar">