Tailwind 4, and configuration that is a stylesheet

A JavaScript configuration file replaced by CSS, which changes what the tool is rather than how it is set up.

what moved:

  tailwind.config.js  →  @theme in a stylesheet
  content globs       →  automatic detection
  the PostCSS chain   →  a single plugin
  @tailwind base      →  @import "tailwindcss"

and what that means: the configuration is now readable
by anybody who reads CSS, rather than by anybody who
reads a JavaScript object with a documented shape.

which is the actual change, and it is larger than the
engine rewrite everybody talked about.

A configuration file in the language of the thing being configured is a real improvement in who can maintain it, and it is the change that made a fourth evaluation worth doing. The engine being faster was the headline and is irrelevant to a project whose build is already under a second.