Based on mdBook's variables.css and ayu-highlight.css, which are based off of the Ayu theme;
original by Dempfi (https://github.com/dempfi/ayu).
This style/colour scheme is generally a bit softer than GitHub's dark theme and also covers GitHub Docs.
It's not required to activate GitHub Dark when using this theme, but I still recommend it to avoid any sudden bright elements where the UserCSS is incomplete.
You can use the Stylus browser extension to use this theme.
Navigate to https://raw.githubusercontent.com/Tamschi/mdBook-Ayu-for-GitHub/main/mdBook-GitHub-Ayu.user.css after installing one of the extensions and you should see a prompt to install the theme. Further updates should be available from the list of installed styles.
Licensed under Mozilla Public License, version 2.0.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this work by you shall be licensed as above, without any additional terms or conditions.