CSS

Dark mode looks like a class you toggle. Then you meet the flash of the wrong theme on load, colors that drift because every component hardcodes its own, and a theme context that re-renders the whole app. Theming done right is tokens, one switch point, and a boundary — and it barely touches React at all.

Styling is the most argued-about, least reasoned-about decision in a React app. The real question isn't which library looks nicest in a demo — it's which one survives a growing codebase. Here's how I weigh Tailwind, CSS Modules, CSS-in-JS, and zero-runtime options, and where each one earns its place.