Visit https://en.wikipedia.org/wiki/Special:Preferences?useskin=minerva when logged in
Notice how the tabs are unstyled:
Also note the save button:
and input widgets:
This is expected as Minerva specifically avoids loading unnecessary CSS and enforcing UI standards and I guess blocked on T117781 but I wonder if there is a way to improve rendering for Minerva... maybe enabling OOUI widgets just for that skin?