The solution is to not overwrite the original link tag in head that refers to style.css. Just add more link tags below it.
Edit: It doesn’t seem to matter what order the links are in. It probably isn’t good practice but putting them anywhere between produces the same page.
Side rant: This exercise will “go green” without checking that everything works. Even if all you see is black/white Times New Roman. If you correctly changed the font in Part 6, however, that WILL go red ^_^.
And threads get locked awfully fast here. There were several closed posts about this without solutions - basically forced duplicates.