This is a simple, Bootstrap-based Sphinx theme from the PyData community. This site is a guide for using the theme, and a demo for how it looks with various elements.
Other sites that are using this theme:
Pandas: https://pandas.pydata.org/docs/
NumPy: https://numpy.org/devdocs/
Bokeh: https://docs.bokeh.org/en/dev/
JupyterHub and Binder: https://docs.mybinder.org/, http://z2jh.jupyter.org/en/latest/, https://repo2docker.readthedocs.io/en/latest/, https://jupyterhub-team-compass.readthedocs.io/en/latest/
Jupyter Book beta version uses an extension of this theme: https://beta.jupyterbook.org
Fairlearn: https://fairlearn.github.io/quickstart.html
Theme Documentation