JSFiddle - React, Tailwind, and code Playground

HTML

<div id="example"></div>
<div id="example2"></div>

CSS

body {background: #999;}
#example{
    background: #aaa;
    -webkit-box-shadow: inset 0 10px 10px #666;
    -moz-box-shadow: inset 0 10px 10px #666;
    width: 300px;
    height: 300px;
    float: left;
    margin-right: 5px;
}

#example2{
    background: #aaa;
background: -moz-linear-gradient(top, #666 0%, #AAA 5%, #AAA 100%); /* firefox */

background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,#666), color-stop(5%,#AAA), color-stop(100%,#AAA)); /* webkit */
    width: 300px;
    height: 300px;
    float: left;
}