[docs] update tailwind installation instruction to v4

docs/01-app/01-getting-started/05-css.mdx

@@ -103,45 +103,22 @@ export default function RootLayout({ children }) {
 
 ### Installing Tailwind
 
-To start using Tailwind, install the Tailwind CSS packages and run the `init` command to generate both the `tailwind.config.js` and `postcss.config.js` files:
+To start using Tailwind, install the necessary Tailwind CSS packages:
 
 ```bash filename="Terminal"
-npm install -D tailwindcss postcss autoprefixer
-npx tailwindcss init -p
+npm install -D tailwindcss @tailwindcss/postcss postcss
 ```
 
 ### Configuring Tailwind
 
-Inside your Tailwind configuration file, add paths to the files that will use the Tailwind class names:
+Create a `postcss.config.mjs` file in the root of your project and add the `@tailwindcss/postcss` plugin to your PostCSS configuration:
 
-```ts filename="tailwind.config.ts" highlight={5-7} switcher
-import type { Config } from 'tailwindcss'
-
-export default {
-  content: [
-    './app/**/*.{js,ts,jsx,tsx,mdx}',
-    // Or if using `src` directory:
-    './src/**/*.{js,ts,jsx,tsx,mdx}',
-  ],
-  theme: {
-    extend: {},
-  },
-  plugins: [],
-} satisfies Config
-```
-
-```js filename="tailwind.config.js" highlight={4-6} switcher
+```js filename="postcss.config.mjs" highlight={4}
 /** @type {import('tailwindcss').Config} */
-module.exports = {
-  content: [
-    './app/**/*.{js,ts,jsx,tsx,mdx}',
-    // Or if using `src` directory:
-    './src/**/*.{js,ts,jsx,tsx,mdx}',
-  ],
-  theme: {
-    extend: {},
+export default {
+  plugins: {
+    '@tailwindcss/postcss': {},
   },
-  plugins: [],
 }
 ```
 
@@ -150,9 +127,7 @@ module.exports = {
 Add the [Tailwind directives](https://tailwindcss.com/docs/functions-and-directives#directives) to your [Global Stylesheet](#global-css):
 
 ```css filename="app/globals.css"
-@tailwind base;
-@tailwind components;
-@tailwind utilities;
+@import 'tailwindcss';
 ```
 
 Then, import the styles in the [root layout](/docs/app/api-reference/file-conventions/layout#root-layouts):