The "cancel" button in the cover art uploader should be styled consistent with the rest of the site and with the negative class (like I did in https://github.com/96187/musicbrainz-server/commit/0d3923b6da94e0ee4791420c3f13f20d5e493377 )

I also think it should be "Remove" and not "Cancel" - you have a list of files and you're removing one from the list, so "cancel" doesn't really work for me there.