These userstyles can be used on any mastodon instance but you'll need to install an userstyle manager on your browser. I recommend Stylus (https://add0n.com/stylus.html) because it doesn't have any tracking and it's libre !
With an userstyle manager on your browser you only need to open userstyles files (click Raw
buttons on GithubGist interface) to use them. Yeah, this install process sucks, sorry.