JSFiddle - React, Tailwind, and code Playground

HTML

<div class="box" id="boxS">
    <ul class="invisible">
      <li>blabla</li>
      <li>blabla</li>
       </ul>
</div>

CSS

.box {
    border: 1px solid black;
    cursor: pointer;
}
.invisible {
    opacity: 0;
}

JavaScript

document.getElementById('boxS').onclick = function(oEvent){
    var list = this.getElementsByTagName('ul')[0];
    if (~list.className.indexOf('invisible')) {
        list.className = list.className.replace('invisible', '');
    } else {
        list.className += ' invisible';
    }
}