JSFiddle - React, Tailwind, and code Playground

HTML

<div class="triangle-with-shadow"></div>

CSS

.triangle-with-shadow {
   width: 100px;
   height: 50px;
   position: relative;
   overflow: hidden;
   box-shadow: 0 16px 10px -15px rgba(0,0,0,0.5);
}
.triangle-with-shadow:after {
   content: "";
   position: absolute;
   width: 50px;
   height: 50px;
   background: #999;
   transform: rotate(45deg);
   -ms-transform:rotate(45deg); /* IE 9 */
   -moz-transform:rotate(45deg); /* Firefox */
   -webkit-transform:rotate(45deg); /* Safari and Chrome */
   -o-transform:rotate(45deg); /* Opera */
   top: 25px;
   left: 25px;
   box-shadow: -1px -1px 10px 0px rgba(0,0,0,0.5);
}