If you’re looking for a good video on the possibilities of Modern CSS (“CSS X”?), check out this talk by Rachel Andrew. She’ll get you up to speed with things:
Over the last few years, rapid browser implementation of advances in CSS have given us the ability to do many of these previously impossible things. We can use our new powers to build the same designs faster, or we can start to ask ourselves what we might do if we were solving these problems afresh.