Stylus is a CSS preprocessor that transforms a dynamic language into standard CSS. It utilizes a compilation workflow to enable the use of variables, nesting, and arithmetic, which are then rendered into stylesheets for use in frontend asset pipelines.
The project is distinguished by a flexible syntax that allows for indentation-based styling, meaning curly braces, colons, and semicolons can be omitted. It further differentiates itself through a JavaScript-driven plugin pipeline and the ability to extend the native syntax with custom JavaScript functions for complex logic.
Its capability surface covers a wide range of authoring tools, including hierarchical selector nesting, reusable mixins, and a comprehensive color management system for mixing and transforming values. The compiler also supports programmatic style generation through mathematical operations, list and hash iteration, and conditional logic evaluation.
The toolset includes a standalone command-line interface for compilation and reverse compilation, as well as middleware for automated CSS updates and source map generation for debugging.