Which CSS frameworks are you using and why?

I've relied mostly on Vanilla CSS and SASS/SCSS so far and have my own components/styles which I can reuse.

But I want to speed up my web development process especially for responsive design. I've tried out Bootstrap in the past but I always found it annoying to work with.

I am attracted to Tailwind.css but it doesn't fit in well with my SASS reliance.

So I am curious ... which frameworks are you using and why?