JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="content"></div>
</div>

CSS

.container{
    position: relative;
    background-color: #f0f0f0;
    padding: 20px;
}

.content{
    height: 200px;
    width: 200px;
    background-color: #fff;
}

.content:after{
    content: "";
    -webkit-box-shadow:  0px 20px 15px -15px rgba(0, 0, 0, 0.49);
    box-shadow:  0px 20px 15px -15px rgba(0, 0, 0, 0.49);
    position: absolute;
    top: 20px; /* .container top padding */
    left: 0; /* 20 - (15/2) = .container left padding - (shadow spread / 2) */
    width: 100%; /* .content width + shadow spread */
    height: 200px;
}