COLORS MIGHT BE BROKEN SINCE GITHUB UPDATED THEIR SITE & FIRA CODE FONT DOESNT WORK ANYMORE
install here -> https://chrome.google.com/webstore/detail/github-stellar-theme/chkkhpmjibgmacpgidnmmdolkdbfheha
recommend using with github 'Dark dimmed' (settings > appearance > theme)
colors can be changed by clicking the extension and click 'settings'
themes can be found here -> https://github.com/frog1123/github-stellar-theme-v2/tree/master/themes