I've now fixed that weird gap in the nav bar. Turns out there was a style property on the images themselves that I don't remember adding so I just didn't notice them. So that's one thing fixed, now if only I knew how to center the links on the nav bar.

After much effort, my website now has a nav bar. It's not quite the way I wanted it because I can't figure out how to centre it or why there's that gap at the bottom, but it works I guess.