You have tried CSS in JS but still have some doubts about deploying it in a large scale application? At Cloudflare, we have started using and migrating to CSS in JS almost two years ago and now it’s a good time to share the lessons we learned! Are you curious about how to pick the right CSS in JS library? What is the best strategy to test your components? Are CSS selectors dead? When and how to use themes? How to educate the rest of organization? How does it fit in a big picture of design systems and component libraries? Oh and if you wonder if React will be mentioned then the answer is YES!