<div id="root"></div>
class App extends React.Component{
  render(){
    return <h1>Hello, world!</h1>;
  }
}

ReactDOM.render(
  <App/>,
  document.getElementById('root')
);
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External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/react/16.9.0/umd/react.production.min.js
  2. https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.6/umd/react-dom.production.min.js