TailwindCSS not working in TypeScript even I already imported

Question

import ReactDOM from 'react-dom/client'
import App from './App.tsx'
import './index.css'
import { BrowserRouter } from 'react-router-dom'

ReactDOM.createRoot(document.getElementById('root')!).render(
    <BrowserRouter>
      <App />
    </BrowserRouter>
)

I had already installed tailwind CSS in the app and put tsx from the settings but even I imported it still does not work with any classes. I checked clearly that I already imported the required classes so I got stuck. May I ask how to change the settings to have the app working with the classes in tailwind CSS?