JSFiddle - React, Tailwind, and code Playground

HTML

<div id="resultsBox">
<ul>
<li></li> // Index 0
<li></li> // Index 1
<li class="selected">// Index 2</li>
</ul>
</div>

CSS

.aaaa { color:#f00 !important; }

JavaScript

$('ul li').each(function(i) {
    if ( i === 2 ) {
       $(this).addClass('aaaa');
    }
});