No, they just have a very thorough understanding of the box model and all the different selectors. There's quite a lot of pieces and they can interact in many ways; some people just have the right mindset to solve that puzzle.
Is there a good advanced css book (or other long-form resource), or do you just have to read specs at this level? I feel like I have "known" CSS reasonably well for quite some time, but have never attained the level of depth it takes to really grok all the ways the puzzle pieces interact with one another.
