Its not enough to know just html & css. Design is more different thing. If you have a nice idea and could sketch on the paper even ordinary web designer could implement that. Dont waste your time with these crap things. Just try be best painter, photographer or illustrator forget the html and other things, just sharpen your design skills.
I understand your sentiment but I know a lot of designers who, while they love what they do, are finding it harder to land non-web gigs. So for them, it may be necessary to learn html/css in order to keep making money at a job that's at least somewhat related to their existing skill set.
