In my day to day work I don't write any css at all, but I still very much enjoyed this blogpost by Adam Wathan where he shares some interesting things about how css should be structured and he makes the case for using utility classes to make visual tweaks.
When you think about the relationship between HTML and CSS in terms of "separation of concerns", it's very black and white.
You either have separation of concerns (good!), or you don't (bad!). This is not the right way to think about HTML and CSS. Instead, think about dependency direction.
One of the biggest benefits of using small, composable utilities is that every developer on your team is always choosing values from a fixed set of options.