Flask-Themes2 is a fork of Spirits, which is in turn a fork of Flask-Themes.
This provides infrastructure for themes in Flask >= 2.0.
To install normally:
$ pip install flask-themes2
To install the development (latest) version:
$ pip install -e git://github.com/sysr-q/flask-themes2.git#egg=flask_themes2-dev
The documentation is on the Flask-Themes2 docs.
If you're interested in helping, the source is available on GitHub, feel free to contribute.