css postcss - [POPULAR] Transforming styles with JS plugins sass - [POPULAR] Sass makes CSS fun! less.js - [POPULAR] Less. The dynamic stylesheet language. normalize.css - A modern alternative to CSS resets emotion - CSS-in-JS library designed for high performance style composition stylelint - A mighty, modern style linter aphrodite - Framework-agnostic CSS-in-JS with support for server-side rendering, browser prefixing, and minimum CSS generation clean-css - Fast and efficient CSS optimizer for node.js and the Web helium-css - Helium - javascript tool to scan your site and show unused CSS jss - An authoring tool for CSS which uses JavaScript as a host language. csscss - A CSS redundancy analyzer that analyzes redundancy.