JSFiddle - React, Tailwind, and code Playground

HTML

<div class="callback">открыть</div>
<div id="callback-popup">

</div>
<div id="bg"></div>

CSS

.callback {display: block;}

#callback-popup {display: none; z-index: 30; background: #fff; box-shadow: 0 0 15px rgba(0, 0, 0, 0.5); top: 40%; left: 30%; position: fixed; margin:0 auto; width: 500px; border-radius: 10px; min-height: 200px;}

#bg {left: 0; top: 0; position: fixed; background: #000; opacity: 0.8; z-index: 20; display: none; min-height: 100%; height: 100%; width: 100%;}

JavaScript

$('.callback')['click'](function () {
    $('#bg')['show']();
    $('#callback-popup')['fadeIn']('slow');
});