Features
- Atomic CSS generation at compile time
- Type-safe styles with full TypeScript support
- Deterministic style merging and composition
- Zero runtime overhead — all work done at build time
- Co-locate styles with components
Pros
- Battle-tested at Meta scale (Facebook, Instagram, WhatsApp)
- Predictable style composition — last applied style always wins
- Tiny CSS output through atomic class deduplication
Cons
- Requires a compiler plugin (Babel or other)
- Newer public release — smaller community than alternatives
- Verbose API compared to utility-first approaches
Overview
StyleX is a CSS-in-JS library created by Meta for building optimized, type-safe UI styles. Unlike runtime CSS-in-JS solutions, StyleX extracts all styles at compile time into atomic CSS classes, resulting in zero runtime overhead and highly deduplicated CSS bundles. It powers Facebook, Instagram, and WhatsApp’s web interfaces.
StyleX’s defining feature is deterministic style composition. When multiple styles are applied to an element, the last style always wins — no specificity wars, no cascade surprises. The compiler generates atomic classes (one class per property-value pair) and deduplicates them across the entire application, keeping CSS bundle sizes small regardless of codebase size.
When to Use
StyleX is the right choice when building large-scale applications where CSS bundle size and style predictability matter, when you want type-safe styles co-located with components, or when you need deterministic style composition across a large team.
Getting Started
npm install @stylexjs/stylex @stylexjs/babel-pluginimport * as stylex from "@stylexjs/stylex";
const styles = stylex.create({
base: { fontSize: 16, color: "black", padding: 8 },
highlighted: { color: "blue", fontWeight: "bold" },
});
function Label({ highlight }: { highlight: boolean }) {
return (
<span {...stylex.props(styles.base, highlight && styles.highlighted)}>
Hello, StyleX!
</span>
);
}