Update app.py

app.py

@@ -586,7 +586,7 @@ def main():
   # css_file1 = CSS_PATH / "div.css"
   # css_file2 = CSS_PATH / "side.css"
   css_file2 = CSS_PATH / "ch.json"
-  if not css_file.exists():
+  if not css_file2.exists():
       shutil.copy("assets/css/ch.json", css_file2)
   #   shutil.copy("assets/css/tree.css", css_file)
   #   shutil.copy("assets/css/div.css", css_file1)