Could these instructions be elaborated a bit? Is it not possible to just install from the admin UI? Thx 
EDIT: I installed via the admin UI and it seems to be working except there doesn’t seem to be anywhere to edit scss now
EDIT: nevermind, I see that is probably expected and you’re showing to edit the theme files directly. I wonder if it could be on the roadmap for this to happen via the admin ui? Like, have a variables editor same as you have a settings editor