Sass

Sass is the most mature, stable, and powerful professional-grade CSS extension language in the world, created by Hampton Catlin in 2006 and developed by Natalie Weizenbaum and Chris Eppstein, providing variables, nesting, mixins, functions, inheritance, control directives, and modular imports that extend CSS with programmable features, adopted by major frameworks including Bootstrap, Foundation, Bulma, and Material Design, with implementations in Dart Sass, Node Sass, and Ruby Sass, and used by millions of websites and development teams worldwide. The variable system enables defining reusable values for colors, fonts, spacing, breakpoints, and any CSS value through dollar-prefixed variables, with support for default values, variable scoping, and interpolation, eliminating the find-and-replace tedium of maintaining consistent values across large stylesheets and enabling single-point updates that propagate throughout the codebase. The mixin and function system enables defining reusable style blocks and computational functions that accept parameters, with mixins generating styles that can vary based on arguments and functions returning values for use in property declarations, enabling complex calculations, color manipulation, responsive sizing, and pattern generation without code duplication. The nesting syntax mirrors the HTML structure, enabling selectors to be nested within parent selectors for readable, maintainable stylesheets that reflect the DOM hierarchy, while the parent selector ampersand enables powerful selector composition including pseudo-classes, sibling selectors, and contextual selectors. The module system through use and forward enables splitting stylesheets into focused modules with namespaced imports. The partial files enable organization. Dart Sass provides the fastest compilation. Designed for frontend developers and design system teams.