Mozilla's latest Nightly builds now come with support for Quantum CSS, dubbed 'Stylo'. The CSS engine has been completely re-written in Rust, and is disabled by default, but can be easily switched on.

The CSS Parser Component takes a CSS document, converts it to an XML document and back again. This product strives to make editing more efficient by using the XML format and by creating an easier ...

CSS-in-JS addresses this problem with component-scoped CSS. Almost all JavaScript frameworks are component-oriented, so generating CSS that is scoped to those components is a natural fit.