This theme displays the top-level TOC elements in the page header,
individual pages in the active section in the left sidebar, and
within-page headers in the right sidebar.

This distinction between top-level elements (e.g., the Getting Started
tutorial, the How-to guides, the API documentation), the section pages
(e.g., each page of the Getting Started tutorial), and page headings
makes the documentation easier to navigate.

As a bonus, the theme supports light and dark versions, and is used by
many popular Python packages (e.g., NumPy, SciPy, Pandas, Matplotlib).