Sass

Sass is a CSS preprocessor language that extends CSS with features such as variables, nesting, mixins, and functions, and compiles to standard CSS. It was created by Hampton Catlin and developed by Natalie Weizenbaum, with the first release in 2006. The name stands for Syntactically Awesome Style Sheets. Sass comes in two syntaxes: SCSS, which uses braces and semicolons and resembles CSS, and the original indented Sass syntax, which relies on indentation rather than braces. Both syntaxes compile to CSS.

Key features include variables for reusable values, nesting of selectors to reflect the HTML structure, mixins and include to reuse blocks of declarations, and extends to share rules across selectors. Sass also provides control structures such as if, for, each, and while, as well as color and mathematical operations. Since its early versions, Sass has evolved a module system using @use and @forward to organize styles without global imports, while partials (files prefixed with an underscore) can be composed.

Sass code is transformed by a compiler into CSS. The official implementation in modern tooling is Dart Sass, available as a command-line tool and as a library for Node-based build systems. Older implementations such as Ruby Sass and LibSass have been deprecated or discontinued. Sass is widely used in front-end development, enabling more maintainable stylesheets through its higher-level abstractions while remaining compatible with CSS.