Tailwind CSS v4 is a utility-first CSS framework that generates styles from HTML/template content at build time. The core engine is written in TypeScript, with a high-performance Rust-based scanner (`crates/oxide`) for fast file traversal and candidate extraction. It is distributed as a monorepo with multiple integration packages: a PostCSS plugin (`@tailwindcss/postcss`), Vite plugin (`@tailwindcss/vite`), Webpack loader (`@tailwindcss/webpack`), Turbopack integration (`@tailwindcss-turbopack`), CLI (`@tailwindcss/cli`), standalone binary (`@tailwindcss/standalone`), and a browser-ready build (`@tailwindcss/browser`). The upgrade tool (`@tailwindcss/upgrade`) automates migration from v3 to v4, covering CSS directives, template syntax, and JS configs. The architecture emphasizes performance through Rust native bindings, a custom CSS parser, and an advanced AST optimization pipeline. The codebase demonstrates exceptional craftsmanship with extensive test coverage, well-abstracted patterns (state machines, AST walkers, value parsers), and a clean separation between core logic and framework integrations. It is actively maintained with frequent releases and a large community.
Tailwind CSS Animated is an npm library that extends Tailwind CSS with a comprehensive set of animation utilities and 19 predefined keyframe animations. It provides utility classes for animation duration, delay, direction, iteration count, timing function, fill mode, play state, and composition, plus ready-to-use animations such as wiggle, shake, fade, flip, jump, and rotate. The package is dual-version: it ships a CSS-first implementation using Tailwind v4's @utility and @theme directives (src/utilities/*.css, src/index.css), alongside a legacy JavaScript plugin (src/compat/*.js, src/index.js) that works with Tailwind v3's plugin API. The architecture cleanly separates the v4 CSS utilities from the v3 compatibility layer, sharing a single theme definition in src/compat/theme.js.