Primer CSS is the CSS implementation of GitHub's design system.
Primer CSS provides a foundation of utility classes and component styles built on Sass that teams can use to maintain visual consistency with GitHub's design language. The project distributes styles through npm as the @primer/css package, allowing developers to import individual modules or the complete stylesheet into their projects by configuring Sass include paths.
The project is in KTLO (keeping the lights on) mode, meaning it prioritizes maintenance of existing utility classes rather than active feature development. Teams should use Primer CSS for foundational styling utilities, but for more complete patterns that combine styling with markup and interactive behavior, the maintainers recommend adopting primer/react for React applications or primer/view_components for server-rendered views. This positioning makes Primer CSS most suitable as a low-level styling layer rather than a comprehensive component library.
Development activity shows consistent maintenance with regular updates to dependencies and documentation. The project maintains a documented release process and development workflow, indicating organized stewardship despite its KTLO status.
