Ask HN: Should a web app UI/UX “designer” be expected to know CSS?

I met a designer of web app UI/UX recently. Their designs were pretty cool and had some impressive transitions, animations and interactions. One in particular caught my attention so I asked how they achieved it in css and they responded "oh, I don't know css or javascript or anything. I just have the developers implement it."

That got me wondering...is it unreasonable for a designer to be expected to implement styles, animations and such? The only other "designers" I've worked with have gone so far as to create stubbed out react components, with a complete UI implementation.