UnoCSS Engine

UnoCSS is an instant on-demand atomic CSS engine created by Anthony Fu, a core team member of Vue and Vite, in 2021, designed as a customizable, flexible, and fast alternative to Tailwind CSS and Windi CSS, providing a rules-based CSS generation system that creates utility classes on-demand at build time, with presets for Tailwind compatibility, attributify mode for HTML attribute-based styling, web fonts, typography, icons, and presets for popular frameworks, achieving build speeds up to two hundred times faster than Tailwind through a highly optimized scanning and generation pipeline. The rules engine uses a function-based API for defining custom CSS rules, where each rule maps a utility class name to a CSS declaration object, with the engine scanning source files for matching class names and generating only the CSS that is actually used, resulting in minimal CSS bundles with zero unused rules, while the presets provide pre-configured rule sets including the Tailwind-compatible preset covering the full Tailwind utility API, the Windi preset, and framework-specific presets for Uno, WebFonts, Typography, Icons, and Tagify. The attributify mode enables writing utility classes as HTML attributes, with the text-center class becoming text equal center as an attribute, reducing template verbosity and improving readability for elements with many utilities. The icon preset supports over one hundred fifty thousand icons from Iconify including Material Design Icons, Font Awesome, Heroicons, Tabler Icons, and custom SVG icons, with icons generated as CSS background or mask images on demand. The variant groups for responsive prefixes. The shortcuts for custom utility composition. The preflights for base styles. The dark mode through class or media. Designed by Anthony Fu. Designed for frontend developers.