CSS is a programming language. From What is a programming language, which is the authoritative answer, and has a score of 44:
This definition does not require a language to be Turing-complete (although it certainly permits any Turing-complete language). This is intentional. Turing-completeness is unnecessary for many problems on this site, and there are interesting non-Turing-complete languages and interesting languages whose status with respect to Turing-completeness is unknown.
If it's turing complete, than it meets all of other criteria for "being a language" automatically. That doesn't mean it's easy to use, but if you can write programs for adding and primality checking in brainfuck, by extension you must be able to in CSS. (And game-of-life for that matter)
Now, as for the "crank" issue. Yes, CSS is not fully automated. However, languages do not have to be automated! We allow vim and
the worse editor emacs, and both of these languages require a user to type the entire program in to "run". But, this is not an issue for a language to be valid or not. As long as a language has the right computational abilities, we can consider it a language, and it is valid for answers on this site.
One can even imagine an entirely mechanical language, that requires turning a literal crank. If such a language were to exist, as long as it could take input and produce output, and there was some reasonable way of scoring it in bytes, I would consider it to be a valid language for the site.