#simplemodal-container a.modalCloseImg {
	background:url(/images/x.png) no-repeat; /* adjust url as required */
	width:25px;
	height:29px;
	display:inline;
	z-index:3200;
	position:absolute;
	top:-15px;
	right:-18px;
	cursor:pointer;
}
<!--[if lt IE 7]>
<style type='text/css'>
	#simplemodal-container a.modalCloseImg {
		background:none;
		right:-14px;
		width:22px;
		height:26px;
		filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(
			src='img/x.png', sizingMethod='scale'
		);
	}
</style>
<![endif]-->
#simplemodal-overlay {background-color:#000;}
#simplemodal-container {background-color:#333; border:8px solid #444; padding:12px;}