In order to contribiute you should fork this repo and on your fork create a new branch, save your changes there. Minifying is done automatically when merged, no need for it manually. When creating a pull request, your CSS is automatically checked for errors. Make sure you name your style file something useful, like qwant-hide-sidepanel.css. Include at least two lines of description for your style eg. when does it activate and when does it change. You may (and should) include URLs. Don't forget the license header (add your name there)!