Update app.py

_js=""" -> js="""

app.py

@@ -25,7 +25,7 @@ with gr.Blocks(theme='ParityError/Anime') as demo:
     dropdown.change(None, dropdown, None, js=js)
     toggle_dark.click(
         None,
-        _js="""
+        js="""
         () => {
             document.body.classList.toggle('dark');
         }