> A big problem with CSS is that you end up making overrides no matter how composable you make the classes. And some simple things (e.g. responsiveness) are unintuitive and / or annoying to do in CSS.

10000% agree with this. I have found that copy/paste until you need to go back and change the same value a few times is worth its weight in salt with CSS. Never has "a poor abstraction is worse than duplicate code" been truer than in CSS.

What I found in my FE days ways that it wasn't until the project shipped and we were iterating on v2 did the actual reusable classes appear.