Follow system color scheme live

The dark-mode script set the .dark class once at load. Subscribe to the
prefers-color-scheme media query so the theme also updates while the page
is open when the OS appearance changes.

Signed-off-by: Émile Ré <emile@probo.com>

apps/compliance-portal/index.html

@@ -14,9 +14,11 @@
 
   <script>
     (function () {
-      if (window.matchMedia && window.matchMedia("(prefers-color-scheme: dark)").matches) {
-        document.documentElement.classList.add("dark");
-      }
+      if (!window.matchMedia) return;
+      var mq = window.matchMedia("(prefers-color-scheme: dark)");
+      var apply = function () { document.documentElement.classList.toggle("dark", mq.matches); };
+      apply();
+      mq.addEventListener("change", apply);
     })();
   </script>