JSFiddle - React, Tailwind, and code Playground

HTML

<div>Arrow casting shadow, pls</div>

CSS

body {
    font: normal 18px sans-serif;   
}
div {
    padding: 20px;
    width: 250px;
    line-height: 50px;
    background: #aaa;
    text-align: center;
    box-shadow: 0 0 4px #000;
    margin: 20px;
    position: relative;
    border-radius: 4px;
}
div:after, div:before {
    content: ' ';
    display: block;
    position: absolute;
    bottom: -10px;
    background: #aaa;
    box-shadow: 0 0 4px #000;
    width: 20px;
    height: 20px;
}
div:before {
    -moz-transform: rotate(45deg);
    -ms-transform: rotate(45deg);
    -o-transform: rotate(45deg);
    -webkit-transform: rotate(45deg);
    transform: rotate(45deg);
}
div:after {
    box-shadow: none;
    border: none;
    bottom: 0;
    left: 10px;
    width: 40px;
    height: 24px;
}