<title>Computed Styles Example</title>
<script type="text/javascript">
function showComputedStyles(){
var myDiv = document.getElementById("myDiv");
var computedStyle = document.defaultView.getComputedStyle(myDiv, null);
alert(computedStyle.backgroundColor);
alert(computedStyle.width);
alert(computedStyle.height);
alert(computedStyle.border);
alert(computedStyle.borderLeftWidth);
alert(computedStyle.visibility);
<div id="myDiv" style="background-color: red; border: 1px solid black"></div>
<input type="button" value="Show Computed Styles" onclick="showComputedStyles()">
<p>(This example won't work in IE < 9.)</p>