JSFiddle - React, Tailwind, and code Playground

HTML

<div class="content">
This is my element with 25% side borders.
</div>

CSS

body {
    padding: 20px;
}
.content {
    border: 1px solid #f00;
}

JavaScript

var el = $(".content");
var width = el.width();
el.css("border-width", "1px " + ((width / 4) | 0) + "px");