JSFiddle - React, Tailwind, and code Playground

HTML

<div id="top1">

<a> <span id="s1" class="myclass">a</span></a>
<i><span id="s2" class="myclass">b</span></i>
</div>

<div id="top2">
   <span id="s1" class="myclass-old">a</span>
   <span id="s2" class="myclass">b</span>
</div>

CSS

.myclass-new{
    background : #f00;
}

JavaScript

$('#top1 span').attr('class', 'myclass-new');