diff --git a/web/dart/theme.dart b/web/dart/theme.dart
index 823a3f9..676bfd2 100644
--- a/web/dart/theme.dart
+++ b/web/dart/theme.dart
@@ -21,8 +21,6 @@ final themes = {
 
 final localStorage = window.localStorage;
 
-var currentTheme = themes[localStorage['theme']];
-
 void enableThemeChanger() {
   final darkBtn = querySelector('#darkBtn');
   final lightBtn = querySelector('#lightBtn');
@@ -34,10 +32,12 @@ void enableThemeChanger() {
 }
 
 Future<void> setTheme() async {
-  if (currentTheme == null) {
-    currentTheme = themes['light'];
-    localStorage['theme'] = currentTheme.getName();
-  }
+  final currentTheme = themes[localStorage['theme']] ??
+      () {
+        final devicePrefersDark =
+            window.matchMedia('(prefers-color-scheme: dark)').matches;
+        return themes[devicePrefersDark ? 'dark' : 'light'];
+      }();
   querySelector('body')
     ..classes.clear()
     ..classes.add(currentTheme.getName());