If the CSS was omitted from my website it wouldn’t function very well either.... But I still think I should be able to hire a web designer on a contract basis to setup my CSS.

This is exactly why I think the ABC test is so disingenuous. It papers over the whole reason contracts are great — providing a single well defined service for a fixed price, and then moving on with life without worrying about a million regulations and forms and paperwork and insurance and hiring practices and workplace blahbity blah.