Useraccounts: How to apply custom design?

Hey guys,

I am using the Useraccounts (+ MaterializeCSS) package on my project and would like to change the design of the forms. However, I couldn’t find anywhere instructions about how to do it: Which HTML files to edit (and where to find them), which CSS classes to change…?

I tried to capture this information by reading the Github source of the package, but couldn’t find a solution…

Has anyone ever done this and could give me a few tips? Thanks!