tailwind-v3-to-v4-migration

Upgrade a codebase from Tailwind CSS v3 to v4. The codemod does ~80% of the mechanical work; this skill supplies the 20% of judgment where migrations actually break — changed defaults, config porting, plugin/animation swaps, and proving nothing moved.

When to use

• Upgrading any project from Tailwind v3.x to v4.x.
• Build errors after a partial upgrade: @tailwind directives unknown, missing @tailwindcss/postcss, Cannot apply unknown utility class, tailwind.config no longer picked up.
• Converting tailwind.config.{js,ts} to CSS-first @theme.

Skip if: the project is already on v4; you need to downgrade; or you are building a brand-new design system rather than migrating one. Note v4 targets Safari 16.4+, Chrome 111+, Firefox 128+ — if you must support older browsers, stay on v3.4 (flag this to the operator before proceeding).

The one idea that makes this safe