JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<div id="app"></div>

CSS

.mystyle {
  width: 100%;
  padding: 25px;
  background-color: coral;
  color: white;
  font-size: 25px;
  box-sizing: border-box;
}

Babel + JSX

class App extends React.Component {
    state = {
        opened: false
    }

    open = () => {
        this.setState({
        opened: !this.state.opened
      });
    };
                            
    render(){
        return (
           <div>
             <button onClick={this.open}>Жми</button>
             <div className={(this.state.opened) ? "mystyle" : ""}>Текст</div> 
           </div>
        );
    }
}

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