<style>
#a {
    position: absolute;
    left: 0px;
    top: 0px;
    width: 100px;
    height: 100px;
    background-color: green;
}

#b {
    position: absolute;
    left: 0px;
    top: 0px;
    width: 100px;
    height: 100px;
    background-color: blue;
}
</style>
<body>
<div id="a"></div>
<div id="b"></div>
<p>The boxes should both be at 0, 0.</p>