I was on the fence of implementing everything myself, but to be honest, why do the same work twice? So I grabbed materialize.css from the good folks that made it. There was a bit of a learning curve, due to the incomplete documentation, but overall, I think it went quite well in just one afternoon.
Give mobile a try, everything scales now properly. I was also able to reduce the amount of HTML tags tremendously. And all of this still runs on Jekyll. I am still confident, that Jekyll is the right System for me. Yes, WordPress has some good stuff, but a static site just offers less attack points and is less work overall.
I really like this design, how it feels, how it looks. I just need to write more articles insert_emoticon.