<div id="root"/></div>

.buttons{
  display:flex;
  justify-content:center;
  margin-top: 50px;
  padding:10px;
}

const App = () => {
    return (
      <div classname="main"> 
        <div className="buttons">
          <button class="button is-success is-small">Small</button>
          <button class="button is-warning is-medium">Medium</button>
          <button class="button is-danger is-large">Large</button>
        </div>
      </div>
    )
}

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