A modern theme for Github. Google's Material Design was kept in mind for most of the project. Keep in mind this is a WIP theme. In this design I tried to put their current content in a fresh and modern look without altering the work flow.
You can go to the theme's page on userstyles and install it directly there or use a 3rd party extension for your browser that will let you customize websites with css and then just paste the theme's css in there.