JSFiddle - React, Tailwind, and code Playground

HTML

<div class="block"></div>

CSS

.block{
    position: relative;
    width: 300px;
    height: 200px;
    margin: 50px auto;
    background: #fff;
    border: 1px solid #ccc;
    border-radius: 15px;
}

.block:after{
    content: '';
    position: absolute;
    bottom: 5px;
    left: 10px;
    right: 10px;
    height: 100px;
    background: red;
    -moz-border-radius: 120px / 50px;
    -webkit-border-radius: 120px / 50px;
    border-radius: 250px / 50px;
    box-shadow: 0px 10px 20px 3px #222;
    z-index: -1;
}