SASS/SCSS

SASS is a CSS preprocessor that extends standard CSS with variables, nesting, mixins, functions, and partials for more maintainable stylesheets. It comes in two syntaxes: the original indentation-based SASS syntax and the more widely adopted SCSS syntax, which uses curly braces and semicolons identical to regular CSS, making any valid CSS file also valid SCSS.

The practical value lies in managing complexity. Variables store reusable values like colors and spacing. Nesting mirrors HTML structure for readability. Mixins encapsulate reusable patterns like media query breakpoints or vendor prefix sets. Partials split styles into modular files that compile into a single output. These features matter most in large codebases where raw CSS becomes difficult to maintain. While modern CSS now includes native variables and nesting, SASS remains widely used because its ecosystem of features, mature tooling, and framework integrations provide capabilities that native CSS has not fully replicated.