...
export default class App extends Component {
  render() {
    return (
      <div className="App">
        <header className="App-header">
          <h1 className="App-title">Welcome to React</h1>
        </header>
        <div className="App-intro">
        <Toggle>
          {({on,toggle}) => (
              <div>
                <button onClick={toggle}>Login</button>
              { on && <Modal>
                <h1>Hello World Modal</h1>
              </Modal>}
              </div>
            )}
        </Toggle>
        </div>
      </div>
  )
  }
}