JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
    width:300px;
    height:300px;
    background:#FFF;
    position: relative;
}
div:before, div:after
{
  z-index: -1;
  position: absolute;
  content: "";
  bottom: 30px;
  left: 10px;
  width: 50%;
  top: 80%;
  max-width:300px;
  background: #777;
  -webkit-box-shadow: 0 35px 20px #777;
  -moz-box-shadow: 0 35px 20px #777;
  box-shadow: 0 35px 20px #777;
  -webkit-transform: rotate(-8deg);
  -moz-transform: rotate(-8deg);
  -o-transform: rotate(-8deg);
  -ms-transform: rotate(-8deg);
  transform: rotate(-8deg);
}
div:after
{
  -webkit-transform: rotate(8deg);
  -moz-transform: rotate(8deg);
  -o-transform: rotate(8deg);
  -ms-transform: rotate(8deg);
  transform: rotate(8deg);
  right: 10px;
  left: auto;
}