Hi follow the instructions available from here

https://tailwindcss.com/docs/installation/framework-guides/nextjs

I have the same issue I resolved by changing

global.css

@import "tailwindcss";

package.json

{
  "name": "yuhop-web",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "dev": "next dev --turbopack",
    "build": "next build",
    "start": "next start",
    "lint": "next lint"
  },
  "dependencies": {
    "next": "15.3.1",
    "react": "^19.0.0",
    "react-dom": "^19.0.0"
  },
  "devDependencies": {
    "@eslint/eslintrc": "^3",
    "@tailwindcss/postcss": "^4.1.4",
    "@types/node": "^20",
    "@types/react": "^19",
    "@types/react-dom": "^19",
    "autoprefixer": "^10.4.21",
    "eslint": "^9",
    "eslint-config-next": "15.3.1",
    "postcss": "^8.5.3",
    "tailwindcss": "^4.1.4",
    "typescript": "^5"
  }
}

tailwind.config.js

/** @type {import('tailwindcss').Config} */
module.exports = {
  content: [
    './app/*.{js,ts,jsx,tsx}',
    './components/**/*.{js,ts,jsx,tsx}',
  ],
  theme: {
    extend: {},
  },
  plugins: [],
};

postcss.config.js

module.exports = {
  plugins: {
    '@tailwindcss/postcss': {},
    autoprefixer: {},
  },
}

page.tax

export default function HomePage() {
  return   <div className="flex h-screen justify-center items-center">
    <div className="text-center bg-blue-400"> 
        <h1 className="text-3xl">HEADING</h1>
        <p className="text-xl">Sub text</p>
    </div>
  </div>}