IE8 CSS width, can't use percents?

Anyone have any problems with this? px 开发者_运维问答and em work fine, % does nothing. I just want to extend this div the length of the screen in IE8. Microsoft, please. Been looking for a while to now avail.

CSS

#topPane {width:100%;
height:100px;
background-color:#0C9;}

HTML

<div id="topPane">a</div>

by popular request :p i post my comment/answer

could it be that you have defined a width for a parent element? like html or body or another div that contains the #topPane ?

If we define width as 100% for parent and 90% fro the child like that further if there are futher childs elements. It should work right???