By leveraging Radix UI and Tailwind, shadcn provides a really powerful combo that works well together.

The defaults are awesome, things mostly just work out of the box and the whole “copy-pasta” concept works surprisingly well in the age of agentic AI.

Bonus points for their builtin CLI tool.

There were other many great tools before it, including Bootstrap, but Tailwind managed to package the most important concepts of functional CSS into an easy to use and framework agnostic tool.

Getting massive adoption from the PHP community (which is doing well and thriving) also did help a lot.