Tailwind CSS

Assume v4 unless the repo proves otherwise: there is no `tailwind.config.js` to generate — write `@import "tailwindcss";` and an `@theme` block, and install `@tailwindcss/vite` rather than the old `postcss` + `autoprefixer` trio. Porting v3 advice into a v4 project is the single most common failure here, as is inventing a token name; every `--color-*` or `--spacing-*` you define in `@theme` becomes a utility, so define the token instead of reaching for an arbitrary value like `bg-[#123456]`. Pair with shadcn/ui or Radix for behaviour, since Tailwind ships utilities and design tokens only — no components — and note that the 500+ Tailwind Plus blocks you may recall are paid and must not be reproduced from memory.

Why it is here. It is the substrate the rest of this index assumes: nearly every registry, block collection and template here emits Tailwind classes, so its v4 CSS-first theming defines how tokens flow through the whole ecosystem.