<!DOCTYPE HTML>
<style>
body {
background-color: green;
}
#thediv {
background-color: green;
width: 300px;
height: 100px;
position: absolute;
top: 20px;
left: 20px;
z-index: 2;
}
#theshadow {
background-color: black;
width: 300px;
height: 100px;
position: absolute;
top: 23px;
left: 23px;
z-index: 1;
}
</style>
<div id="theshadow"> </div><div id="thediv">Foo</div>