In Tailwind v4 you can’t use just `@import "tailwindcss";`.

Replace it in `globals.css` with:

@import "tailwindcss/base";

@import "tailwindcss/components";

@import "tailwindcss/utilities";

Also remove the const config = {...} part from CSS (that belongs in config files).
Then keep only import './globals.css' in app/layout.js → your global styles will work.