Ask HN: Good ressources to learn (Web-)Design

I am a solid Programmer and I know pretty much all I need to know about Backend- and Frondend-Developing. But I would like to get deeper into the Design-Aspect. I am not talking about HTML, CSS, etc.. More about what makes a good Design actually a good Design. I already read "Don't make me think" and "The Design of everyday things", but they were more about usability then actually what makes a design beautiful. Any recommendation what (online-)sources I should try to teach myself?