Move the dark class up to the html element

To get the correct `color-scheme`.

Fixes #2918

assets/js/alpinejs/stores/nav.js

@@ -87,8 +87,8 @@ export function initColorScheme() {
 
 const toggleDarkMode = function (dark) {
 	if (dark) {
-		document.body.classList.add('dark');
+		document.documentElement.classList.add('dark');
 	} else {
-		document.body.classList.remove('dark');
+		document.documentElement.classList.remove('dark');
 	}
 };