CSS-in-JS is a design pattern that addresses challenges in scaling CSS by using JavaScript modules for smaller file separation and unique local naming for scoping. However, this approach can lead to increased loading times as modern UI libraries like React rely on JavaScript bundles, which can grow significantly. Compiled, a library developed by Atlassian Labs, offers a solution by analyzing code at build time and transforming it into components that do not generate CSS at runtime, thus resolving performance issues associated with dynamic CSS generation. It mimics styling patterns from libraries like styled-components and Emotion and allows seamless integration without additional configuration. To use Compiled with React, developers need to install specific packages and plugins for Babel or TypeScript compilers, ensuring efficient styling without runtime costs.