Somethin up with my css

programming web dev
1

I am making an overlay window and in IE6 and 7 when it comes on my page shifts up. It works fine in firefox and IE8.

Here is the link
http://ronnieswietek.com/cc/modal/

here is my css…dimm is the overlay


body {
	height:100%;
	padding:0px;
	margin:0px;
	font-family:Verdana, Arial, Helvetica, sans-serif;
	font-size:11px;
	background-image:url('../images/pattern.jpg');
}

li
{
	list-style-image: url("../images/bullet2.gif");
}

#wrapper {
	width:850px;
	background-color:#E6E6E6;
	margin:15px auto;
}

#content {
	width:800px;
	margin:0px auto;
	padding:15px;
}

.aLink {
	text-decoration:underline;
}

.aLink:hover {
	cursor:pointer;
}

.dimm {
	width:100%;
	height:100%;
	position:absolute;
	top:0;
	left:0;
	display:block;
	background:#000;
}

anyone know whats up here? I suck at css