styled-jsx is a CSS-in-JS library and styling framework for JSX components. It functions as a scoped CSS engine that uses compile-time transformations to generate unique class names, preventing style leakage between components.
The system includes a server-side CSS renderer that flushes styles into HTML to prevent layout flicker during the first paint. It ensures security compliance by attaching per-request nonces to generated style tags to satisfy Content Security Policy requirements.
The framework covers global CSS management with deduplication, dynamic styling via template interpolation, and modular organization through external style definitions. It also provides mechanisms for targeting third-party components and transforming styles at compile time using plugins.