why the js code can't control the css code?
<pre><code>&lt;script&gt;
        var divBgTop=0;
        function initDivTop()
        {
                divBgTop=document.getElementById("divBg").style.pixelTop;
                alert(divBgTop);
        }
&lt;/script&gt;
&lt;style&gt;
.divBgCss
{
        position:absolute;
          left:100px;
    top:100px;
    width:100px;
    height:100px;
        background-color:red;
}
&lt;/style&gt;
&lt;body onload="initDivTop()"&gt;
&lt;div class="divBgCss" id="divBg"&gt;&lt;/div&gt;
&lt;/body&gt;
</code></pre>

<p>the result is always 0. why?</p>
