diff --git a/templates/base.html b/templates/base.html
index 39183f8..8e6fba0 100644
--- a/templates/base.html
+++ b/templates/base.html
@@ -4,6 +4,13 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>{% block title %}Chatroom{% endblock %}</title>
+    <script>
+        // Set theme immediately to prevent flash
+        (function() {
+            const savedTheme = localStorage.getItem('theme') || 'light';
+            document.documentElement.setAttribute('data-theme', savedTheme);
+        })();
+    </script>
 
     <!-- Include highlight.js library for syntax highlighting -->
     <script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.6.0/highlight.min.js"></script>