CSS Frameworks

CSS frameworks have been around a while the most popular by far is Bootstrap the current version is v4.5.3 with version 5 currently in alpha. It's easy to get started with and the documentation is great.

TailwindCSS is slightly different as its a utility-based framework without pre-built components that Bootstrap has.

These are the two I have experience with many other including Materialize, Bulma (flexbox based)