W3Schools Tryit Editor

main.jsx

index.html

import { createRoot } from 'react-dom/client'

createRoot(document.getElementById('sandy')).render(
  <p>Welcome!</p>
)

<!doctype html>
<html lang="en">
  <body>
    <header id="sandy"></header>
    <script type="module" src="/src/main.jsx"></script>
  </body>
</html>