Muro CSS (.mss preprocessor)

A TypeScript CSS preprocessor and bundler for .mss files. Current stable version is 26.0.2. Actively maintained with regular releases. Compiles a single entry file or an entire directory of .mss sources into one CSS output. Supports variables, nesting, mixins, imports (including built-in modules like muro:reset), conditionals, loops, theme baking (light/dark), semantic layering, guard locks, and automatic raster asset rewriting to webp. Includes CLI with watch, minify, purge, sourcemap, and asset-dir options. Ships TypeScript types. Differentiators: designed as a TypeScript-first alternative to Sass/PostCSS with built-in utilities and zero-config polyfilling.