<div id="app"></div>

.des {
  color: red;
}

    class HelloWorld extends React.Component {
        render () {
            return (
                <div>
                    <h3>Hello</h3>
                    <p className='des'>Nice to meet you!</p>
                </div>
            )
        }
    }

    class App extends React.Component {
        render () {
            const headerStyle = {
              color: 'orange',
              fontSize: '3rem',
              textDecoration:'underline'
            }
            return (
                <div>
                    <h1 style={ headerStyle }>React Demo App</h1>
                    <HelloWorld />
                </div>
            )
        }
    }

    ReactDOM.render(
        <App />,
        document.getElementById('app')
    )