Web Compatibility Support • Re: https://windhawk.net/

also how do i put this in a userscript? is this like a script in greasemonkey?

This is a user style,similar to a userscript but CSS and not Javascript. For this the easiest way is to install Stylem. It's a userstyle manager just as Greasemonkey is a userscript manager. It will also add a section in the addons page for itself where you can manage all installed CSS styles.