Install
    npm install -D tailwindcss@^3.3.7 autoprefixer@^10.4.16 @tailwindcss/postcss@latest
    
    package.json{
      "dependencies": {
        "react": "^19.1.0",
        "react-dom": "^19.1.0"
      },
      "devDependencies": {
        "@tailwindcss/postcss": "^4.1.7",
        "autoprefixer": "^10.4.21",
        "parcel": "^2.15.1",
        "react-router-dom": "^7.6.0",
        "tailwindcss": "^3.4.17"
      }
    }
    
    
    create .postcssrc.json in root directory
    
    //.postcssrc.json
    {
      "plugins": {
        "tailwindcss": {}
      }
    }
    
    
    create tailwind.config.js in root directory
    //tailwind.config.js
    /** @type {import('tailwindcss').Config} */
    module.exports = {
      content: [
        "./src/**/*.{js,jsx,ts,tsx}",
        "./public/index.html",
      ],
      theme: {
        extend: {
          colors: {
            primary: '#FF0000', // Custom primary color
          },
          fontFamily: {
            sans: ['Graphik', 'sans-serif'], // Custom font family
          },
        },
      },
      plugins: [],
    }
    
    install  Tailwind CSS IntelliSense Extension 
    
    [enter image description here][1]
    
    

Dont Forget to add it in index.css
@tailwind base;
@tailwind components;
@tailwind utilities;

and link it in index.html
<link href="../src/index.css" type="text/css" rel="stylesheet" />