I didn't run this, but it should be mostly correct.

example.jsx

import React from 'react';
import ReactDOM from 'react-dom';

class ExampleClass extends React.Component {
	constructor(props) {
		super(props);
		this.state = {
			isClicked: false;
		};
	}
	
	handleClick() {
		this.setState({
			isClicked: !this.state.isClicked
		});
	}
	
	render() {
		return (
			<div className='container'>
				<div id='someElement' className={this.state.isClicked ? 'clicked' : ''}>
					I'm an element.
				</div>
				<button id='someButton' onClick={this.handleClick}>
					Click me!
				</button>
			</div>
		);
	}
};

ReactDOM.render(
	<ExampleClass />,
	document.getElementById('content')
);