A CSS utility framework that relies on functional classes and composition to do CSS. It pairs well with a component based approach like React, Svelte and Vue because your markup can contain a lot of classes. Everything that might go into CSS will now be directly inline, much like CSS-in-JS solutions.
Tailwind CSS is my preferred CSS framework for new projects. I choose it over plain CSS because it has good defaults, extensible, consistent and perfect for rapid prototyping.
Tailwind CSS might just be worth your time, especially in teams and in agencies. It makes building easy and is a lightweight design system to get you started.