diff --git a/fastchat/serve/gradio_web_server_multi.py b/fastchat/serve/gradio_web_server_multi.py
index 642380bdd..db5f80293 100644
--- a/fastchat/serve/gradio_web_server_multi.py
+++ b/fastchat/serve/gradio_web_server_multi.py
@@ -135,7 +135,13 @@ def build_demo(models, elo_results_file, leaderboard_table_file):
             + single_model_list
             + side_by_side_anony_list
             + side_by_side_named_list,
-            _js=load_js,
+            _js="""
+        () => {
+            document.body.classList.toggle('dark');
+            document.body.classList.toggle('light');
+            document.querySelector('gradio-app').style.backgroundColor = 'var(--color-background-primary)';
+        }
+        """,
         )
 
     return demo