Update app.py

app.py

@@ -587,7 +587,7 @@ def main():
   # css_file2 = CSS_PATH / "side.css"
   css_file2 = CSS_PATH / "ch.json"
   if not css_file2.exists():
-      shutil.copy("assets/css/ch.json", css_file2)
+      shutil.copy("css/ch.json", css_file2)
   #   shutil.copy("assets/css/tree.css", css_file)
   #   shutil.copy("assets/css/div.css", css_file1)
   #   shutil.copy("assets/css/side.css", css_file2)