Nah. :)
I've used CSS exactly and only once since starting to use this place, just to double the font size of a couple of sentences for ULTRA EMPHASIS.
Otherwise, I've just used Markdown! Markdown takes care of nearly all your formatting needs here and it's loads easier to learn and use than HTML+CSS. And this is coming from someone who does casual web dev as an enthusiast hobby.
You can get by on here just fine without CSS if you don't know how to use it, or if it's too hard to learn. This feature exists for those who want to have fun playing around with it. You don't have to make a CSSplash on this site.
You can get by just fine. π