It depends on where that developer was slotted in.
We currently have ~3 dedicated front end developers who have limited skills beyond HTML, CSS, and Javascript who maintain our large forward facing public presence.
The remainder of our developer pool are full stack developers who maintain a myriad of internal systems and apps used to run the business. A few of these apps are publicly accessible but they're niche and don't require strict adherence to brand or accessibility standards. The remainder are simply internal applications.
A firm grasp of CSS would seem to be essential to the front end devs, though I might be inclined to say it's not given some of the code I've seen. I am however willing to give them the benefit of doubt because I know they're a newer team that inherited an unfathomably large site running on an ancient CMS (Stellent) and the new products they're working on are integrated with some pretty heinous 3rd party platforms.
For the remainder of our Devs usability and appearance take a back seat to functionality. So CSS chops are more of a nice to have.