Now oldschool github addon provides userstyle in their repo: https://raw.githubusercontent.com/daattali/oldschool-github-extension/master/css/osgh.user.css
Relevant issue: daattali/oldschool-github-extension#30
Now oldschool github addon provides userstyle in their repo: https://raw.githubusercontent.com/daattali/oldschool-github-extension/master/css/osgh.user.css
Relevant issue: daattali/oldschool-github-extension#30