I prefer https://tachyons.io/ as a CSS framework that avoids any pre-styled themes and just provides building blocks. Great for SPA/component UIs.
I really do hate to be the guy this guy, but after having to maintain a website a contractor built in Tachyons, I've hated it with a passion of [insert hyperbolic phrase here]. What do you love about it/what am I missing? For me it felt like a tutorial on the most egregious CSS/dom anti-patterns, and I haven't been able to get past it.
It also removes the need to constantly reference CSS at all, and can just stick to HTML/JSX instead. It can get very verbose though, but that's a minor trade-off I think.