How to set the default theme from Light to Custom

I’ve created a default theme for JupyterLab extension. I want to set it as a default so that user dose not have to manually change it. It should activate while Jupyterlab starts.

A package can ship a file in {sys.prefix}/share/jupyter/lab/settings/overrides.d/ which will override any values not set by the user, as if it were the new default.

If a user has already chosen a theme, this will not undo that choice, and overwriting the actual user settings file is a… really bad idea.

So {sys.prefix}/share/jupyter/lab/settings/overrides.d/my-fancy-theme.json:

  "@jupyterlab/apputils-extension:themes": {
    "theme": "My Fancy Theme"

The my-fancy-theme-0.1.0.whl package delivers this to the right location with data_files in or… however the build system du jour does it today.

For some background, this was added on this PR, which contains more links to other issues and some related packages.