StyleX: A Styling Library for CSS at Scale

This post introduces StyleX, Meta's new styling system for large-scale applications. StyleX addresses historical challenges with CSS at Meta, such as collisions, dependency management, and specificity wars, by compiling styles at build time into collision-free atomic CSS. It offers an expressive and type-safe approach to style authoring, combining CSS-in-JS ergonomics with static CSS performance. The post details StyleX's compiler, its core APIs (stylex.create, stylex.props), and its principles of scalability, expressiveness (shareable values, styling at a distance, preserving CSS features), and predictability, making it the default styling system across Meta products.