JSFiddle - React, Tailwind, and code Playground

HTML

<div class="un__shadow">
    <h1>Some details</h1>
    <p>Some content.</p>
</div>

CSS

* { margin: 0; padding: 0; }
body { margin: 50px; }


.un__shadow {
    display: block;
    position: relative;
    z-index: 2;
    width: 200px;
    height: 200px;
    padding: 20px;
    border: 1px solid #ccc;
    background: #fff;
}

.un__shadow:before {
    content: '';
    position: absolute;
    width: 100%; height: 100%;
    bottom: -4px; right: -4px;
    border: 1px solid #ccc;
}

.un__shadow:after {
    content: '';
    position: absolute;
    width: 100%; height: 100%;
    bottom: -6px; right: -6px;
    border: 1px solid #ccc;