There can be - it all depends. If you have a good knowledge of document structure, then half your work will be done for you: you're already used to putting headings in H* tags, for example. If you don't find it easy to think structurally, you might have a slightly harder time of it.

CSS is a pretty powerful tool. It's a bit like Photoshop: you may be really good at using 10-290% of all of its features, but there are always extra things to learn. That's both the joy and the curse