JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
        <span class="iconset"></span> <!-- primeiro elemento -->
        <span class="iconset"></span>
    </div>
    <div class="container">
        <span class="iconset"></span> <!-- primeiro elemento -->
        <span class="iconset"></span>
    </div>

<pre></pre>

CSS

.iconset {
    width: 50px; height: 50px;
    display: inline-block;
    background-color: #000;
}

JavaScript

var elementos = $(".container .iconset:nth-child(1)");

elementos.css("background-color", "red");

$("pre").text(elementos.length);