I'm glad I was able to help!!
I'd probably go ahead and brush up on your HTML/CSS as what you're describing doesn't sound too hard! You'll probably find it easier to customize the look for Twine, too! Although Renpy is a great engine as well, and it isn't terribly hard to learn— it's just more of a pain to customize (and I speak from experience.)
If you're interested, I've been considering writing a guide for Twine— maybe I'll do it when I'm not sleep-deprived, but if that sounds helpful, I can do a rough draft some time and forward it to you.