Frameworks aren't at odds with knowing CSS or any other language. You're missing the point with "CSS isn't hard!"

And you're wrong. CSS is incredibly hard to maintain. It easily becomes an append-only list of rules. Medium.com for example hired a team a CSS developers including a co-creator of Bootstrap just to work full-time on its CSS.

This is a good example of developer hubris and the HN trope of "it isn't that hard, why don't other idiot devs just do <X>? It must be because they're incompetent." I'm not convinced you've drunk your own Kool-aid in production on a non-trivial project. Because then the trade-offs would be obvious to you and you wouldn't think one is better.