Tailwind CSS 4

Picture this: you run the upgrade tool. It finishes without a single error. You breathe a sigh of relief and move on.Two weeks later, a support ticket comes in. A button's shadow looks wrong. A border has quietly turned invisible on a specific browser. Your dark mode toggle flickers for half a second before settling. None of it shows up in your build logs. None of it throws an exception. It's just there, sitting in production, waiting for a user to notice before you do.This is exactly what happens when a migration is treated as a checklist instead of a process. This book exists so that doesn't happen to you. Every breaking change in Tailwind 4 is covered here with the why behind it, not just the what, so you're never left guessing why something looks different after an upgrade that technically "succeeded."What's Inside- The architectural shift behind Tailwind 4's new engine and CSS-first configuration- A full comparison between tailwind.config.js and @theme, token by token- Every renamed, removed, and redesigned utility class, explained clearly- Building real multi-theme systems and dark mode that scale beyond a simple toggle- Container queries, fluid typography, and accessibility-aware responsive design- Writing custom utilities and variants directly in CSS, no JavaScript plugin required- A complete, step-by-step migration playbook, plus the pitfalls that catch real teams- A full case study migrating a realistic production codebase from start to finish- A quick-reference appendix for fast lookups mid-migrationWho It's Meant ForThis book is for you if: - You've built real projects in Tailwind 3 and now need to move to version 4- You want to understand why something changed, not just memorize a rename table- You're responsible for a production codebase and can't afford a…