Add dark mode (#199)

* Add passive dark mode to everything but codemirror

* Add dark theme support for Codemirror

* Make theme a user setting

* Fix button text size

* guard against undefined window

* Formatting and test fix

src/components/Toggle/Toggle.module.css

@@ -18,6 +18,10 @@
   height: calc(var(--toggle-size) + var(--padding));
 }
 
+:global(.dark) .toggle > span {
+  @apply border-chalkboard-40;
+}
+
 .toggle > span::after {
   content: '';
   @apply absolute w-4 h-4 rounded-sm bg-chalkboard-110;
@@ -27,6 +31,10 @@
   transition: translate 0.08s ease-out;
 }
 
+:global(.dark) .toggle > span::after {
+  @apply bg-chalkboard-10;
+}
+
 .toggle input:checked + span::after {
   translate: calc(50% - var(--padding)) -50%;
 }