Tailwind Css V4+Nextjs 15

Tailwind CSS v4 introduces the Oxide engine, a high-performance rewrite that transitions the library from a JavaScript-heavy configuration to a CSS-first approach. In Next.js 15, which defaults to React 19, this integration is handled via the @tailwindcss/postcss plugin. Instead of the traditional tailwind.config.js, developers now define themes and variables directly within their global CSS file using the @theme directive. This significantly reduces the build-time overhead for large-scale Next.js applications.

While Next.js supports Turbopack, the Tailwind v4 integration relies on the postcss.config.mjs file to hook into the compilation process. This ensures that utility classes are correctly extracted from both Client and Server Components. Developers should note that the v4 engine automatically scans all files in the project, eliminating the need for the manually maintained content array in most Next.js 15 setups.