How to complete interface customization

After I use cookiecutter to create an extension, I don’t know where to put the incomplete json in the document to achieve the effect in the example

what should I do

  1. This usually goes into Advanced Settings Editor (JSON), not an extension seeded from a cookiecutter.
  2. The page you linked is for the latest version which is 4.0 alpha (30-something as of today). A lot of these customizations are not available in the current stable 3.x release series.
  3. If you do not want to manually go to Settings → Settings Editor → JSON Settings Editor → JupyterLab Shell → {edit/enter your JSON} (e.g. you are managing JupyterLab for hundreds of users) you may want to use overrides.json.