🚸 Use default system theme (#80)

src/app.html

@@ -16,7 +16,10 @@
 		<div class="contents h-full">%sveltekit.body%</div>
 	</body>
 	<script>
-		if (localStorage.theme === "dark") {
+		if (
+			localStorage.theme === "dark" ||
+			(!("theme" in localStorage) && window.matchMedia("(prefers-color-scheme: dark)").matches)
+		) {
 			document.documentElement.classList.add("dark");
 		}
 	</script>