JSFiddle - React, Tailwind, and code Playground

HTML

<div class="el">bla bla</div>
<div class="el">bla bla 123</div>

CSS

.el {color: blue}

JavaScript

var el = document.getElementsByClassName('el'),
    i;

for (i = 0; i < el.length; i += 1) {
    el[i].style.color = 'red';
}