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/_header.css

@@ -1,53 +0,0 @@
-/* Branding header */
-
-.header {
-  --header-gap: var(--spacing-s);
-
-  padding-block: min(var(--gutters), var(--spacing-m));
-  display: flex;
-  flex-direction: column;
-  gap: var(--header-gap);
-  background-color: var(--color-header-bg);
-
-  @media (min-width: 666px) {
-    flex-direction: row;
-    align-items: center;
-  }
-}
-
-/* Wrapping link for logo. */
-.header__logo {
-  width: fit-content;
-}
-
-/* Logo image. */
-.header__logo-image {
-  vertical-align: bottom;
-}
-
-/* The name of the website. */
-.header__site-name {
-  margin: 0;
-  line-height: 1;
-}
-
-/* The link around the name of the website. */
-.header__site-link {
-  &:link,
-  &:visited {
-    color: var(--color-text);
-    text-decoration: none;
-  }
-
-  &:hover,
-  &:focus {
-    text-decoration: underline;
-  }
-}
-
-/* Wrapper for any blocks placed in the header region. */
-.header__region {
-  @media (min-width: 666px) {
-    margin-inline-start: auto;
-  }
-}