Update app.py

app.py

@@ -67,7 +67,8 @@ def main_app():
         # === Toggle Dark Mode Logic ===
         def toggle_theme(current_theme):
             new_theme = "dark" if current_theme == "light" else "light"
-            return app.set_theme(new_theme), new_theme
+            app.add_body_class(f"{new_theme}-mode")
+            return new_theme
 
         darkmode_btn.click(
             fn=toggle_theme,