Many thanks!
Why? - it is easy, simple to learn and stable. It gives you a solid basic structure and responsiveness as well as looking modern and being easy to customize.
Long time ago I was using https://github.com/twbs/bootstrap for work primarily and https://github.com/foundation/foundation-sites for side projects. Nowadays I use Bulma for everything
p.s. I still don't get the hype around https://github.com/tailwindlabs/tailwindcss ¯\_(ツ)_/¯
But what I do use sometimes is a CSS reset like https://github.com/necolas/normalize.css
And what I also use is this CSS boilerplate: https://github.com/frontaid/natural-selection (Disclaimer: I created it because I wanted to avoid the repetitive work of writing out all the selectors).
website: https://frontendor.com/preview