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/_htmx-indicator.css

@@ -0,0 +1,45 @@
+.htmx-indicator {
+  position: fixed;
+  inset: 0;
+  width: 100%;
+  height: 4px;
+  background: linear-gradient(
+    90deg,
+    transparent,
+    var(--color-accent),
+    transparent,
+    var(--color-accent),
+    transparent
+  );
+  opacity: 0;
+  visibility: hidden;
+
+  &.htmx-request {
+    opacity: 1;
+    visibility: visible;
+    animation:
+      --fadein 2s linear forwards,
+      --slide 1.2s ease-in-out infinite;
+  }
+}
+
+@keyframes --slide {
+  0% {
+    transform: translateX(-100%);
+  }
+  100% {
+    transform: translateX(100%);
+  }
+}
+
+@keyframes --fadein {
+  0% {
+    opacity: 0;
+  }
+  50% {
+    opacity: 0;
+  }
+  100% {
+    opacity: 1;
+  }
+}