JSFiddle - React, Tailwind, and code Playground

HTML

<div class="radius"></div>

<br><br>
    
    <button>Get Radius</buttton>

CSS

.radius {
    background: #333;
    border-radius: 5px;
    width: 200px;
    height: 40px;
}

JavaScript

$('button').on('click', function() {
    alert($('.radius').css("borderTopLeftRadius"));
});