Indeed, I just figured I'd share the full setup. IIRC, Stylus was derived from "Stylish", which was a hugely popular CSS override extension that became spyware around 2016 and was taken down in 2018, and now Stylus (and others of course) fill the gap. It would be very nice to have this integrated into the browser, I agree.

Opera had this in 2003, but sadly none of the major browsers copied it.

I still miss Omniweb, a browser with user defined stylesheets, per site settings, and workspaces… so many good things. Free browsers killed it off.