Nothing too much to expect, these are just two simple dark styles for Studium (and its archive) and Smart_Edu.
As said before, there are two indipendente style, you could install both or only the one you need.
Just download one of these extensions according to your browser
And now click in the UserStyle you'd like to install
Automatically the extension you installed before should recognize the UserStyle and automatically prompt to import it.
To check if there's a new version you have to open your browser and select Stylus, once the popup shows, click Manage.
In the Manage Page just click Check all styles for upates and wait for the magic ✨
Just open the app and it will update each style automatically