postcss

PostCSS is a tool for transforming CSS with JavaScript plugins, serving as the foundation for many modern CSS processing workflows. Unlike Sass or Less which are complete preprocessor languages, PostCSS is a platform that runs plugins to analyze, lint, transform, and optimize CSS. Each plugin performs a specific transformation — Autoprefixer adds vendor prefixes, postcss-preset-env enables future CSS syntax, cssnano minifies CSS, postcss-import inlines @import statements, and postcss-nested enables Sass-like nesting. PostCSS parses CSS into an abstract syntax tree (AST), passes it through configured plugins, and generates the output CSS with source maps. This plugin architecture means you include only the transformations you need, keeping the processing pipeline lean. PostCSS is used internally by Tailwind CSS for its JIT compilation, by Vite and webpack for CSS processing, and by Next.js for its built-in CSS support. The postcss-preset-env plugin is particularly important — it lets you write modern CSS syntax (nesting, custom media queries, color functions) that gets compiled to browser-compatible CSS, similar to how Babel works for JavaScript. PostCSS processes CSS faster than Sass due to its JavaScript-native implementation and focused plugin approach.