## The Next Evolution of Utility CSS Tailwind CSS v4 is a ground-up rewrite engineered in Rust. It eliminates `tailwind.config.js` entirely in favor of native CSS syntax powered by `@theme` directives and cascade layers. ### 1. CSS-First Design Tokens Defining custom typography, color tokens, and animation curves now happens directly inside `globals.css`: ```css @import "tailwindcss"; @theme { --font-editorial: "Plus Jakarta Sans", sans-serif; --color-brand-primary: hsl(265 85% 60%); --color-surface-glass: hsl(240 10% 4% / 0.8); --radius-card: 1rem; } ``` ### 2. Native CSS Container Queries Breakpoints based solely on viewport width are no longer sufficient for modular component architecture. Container queries allow a post card to re-layout from vertical to horizontal based on its immediate parent container's width, not the whole window. ### 3. Build Times Slashed by 10x By ditching Babel and heavy PostCSS plugins, development recompilations drop from hundreds of milliseconds to single-digit milliseconds, making UI design truly feel real-time.