Fix theme reloading on gradio-lite demos.

templates.py

@@ -64,11 +64,14 @@ def load_js(demo_type: DemoType) -> str:
 
 
 def update_iframe_js(demo_type: DemoType) -> str:
-    # TODO: Theme changes are not picked up; look at options to refresh the css.
     if demo_type == DemoType.GRADIO:
         return f"""async (code) => {{       
                 async function update() {{
-                    const appController = document.getElementById('gradio-iframe').contentWindow.window.appController;
+                    // Remove existing stylesheet so it will be reloaded;
+                    // see https://github.com/gradio-app/gradio/blob/200237d73c169f39514465efc163db756969d3ac/js/app/src/lite/css.ts#L41
+                    const demoFrameWindow = document.getElementById('gradio-iframe').contentWindow;
+                    demoFrameWindow.document.querySelector("head style").remove();
+                    const appController = demoFrameWindow.window.appController;
                     const newCode = code + ` # Update tag ${{Math.random()}}`;
                     appController.run_code(newCode);
                 }};