I’m sure this won’t be the only "css" sucks comment.
You missed the absence of any sort of variables/constants to let you (e.g.) assign a logical name to a frequently used colour or a standard indent width. Preprocessors like "less" are a great help, of course, but I can't believe a simple macro substitution facility or simple expression evaluation would have over-taxed even 20 year-old hardware.
Then there's the bizarre box model where the size of the contents, border, inner and outer margin are all conflated - even Microsoft's mis-implementation made more sense. Or the simple, but completely non-obvious incantations to make a div act as a container, or auto-clear floats. I still can't get my head around list formatting.
Basically, you're left with the feeling that the designers of CSS had never used a DTP package, never used styles in a wordprocessor package, never used a UI layout manager or, for that matter, ever seen a website.
TFS was also right on the money in one respect: a standard with neither a test suite or a reference implementation is no standard at all. The whole set of web standards suffers from the delusion that (maybe outside of pure mathematics) you can reliably specify a complex system without non-trivial exemplification.