React script is found but it won’t render the simple hello world element

I’m new to react and i’m just testing out a simple render at the moment. I get no errors in the browser but nothing shows up on my screen that appears in my javascript react file.

html

<html>
    <head>
         <script  type="text/babel" src="reactfile.js"> testing</script>
    </head>
<link rel="stylesheet" href="/styles.css">
<body id="app">
    <p>react test</p>
</body>
</html>

react javascript file

import React from 'react';
import ReactDOM from 'react-dom';
class Helloworld extends React.Component {
  render() {
    return (
      <div>
        <p>Hello world!</p>
      </div>
    );
  }
}

ReactDOM.render(<Helloworld />, document.getElementById('root'));