I just bought a ton of courses on graphical design, typography, etc. off of udemy due to that $10 sale. It's easy to get into the zone where you only want to work on one side of the stack, but if you really want to be marketable, I think you should have skills on both the front-end and the server-side. It's hard for someone, especially if they aren't a programmer themselves, to appreciate what you've created if your sites look like atrocious. One that seems to be a solid course on udemy is here:
Graphic Design Hero: Apply Graphic Design in Projects
Searching for courses on typography is very helpful as well. The coupon to get your discount is 'warmup10'. I think the last day for the sale is tomorrow.
Design Beautiful Websites with Web Typography (2015)