Docs :: Browser Support

mCSS targets Baseline 2024.

It uses cascade layers (@layer), nesting, :has(), and other modern CSS features natively, with no polyfills. In practice that means the versions of Chrome, Edge, Firefox, and Safari that shipped late 2024 and after:

If you install mCSS with the PostCSS option, it is possible to modify mCSS browser support via the .browserslistrc file. Using a different target, postcss-preset-env will start polyfilling the newer features. But it’s not recommended: it will create file bloat and it’s not foolproof. Some features can break in the process. (See this blog post for details on what can break when changing the default browser support.)