Whenever I see on someones resume mentioning CSS as one of their skills i giggle to myself. They can't be serious? CSS is not a programming language! All you need to do is just google a few stuff and copy paste!.
I guess that's why even after ~5 years of developing websites, I would still rate my CSS as below average(way below to be honest).
Although it's true that CSS is not a programming language, but it's still a language nonetheless. A style sheet language and like any other language, you need to take it seriously in order to be good at it.
So, sorry CSS. I promise to take you more seriously next time.