trouble moving a pop up to the centre of the page

<style>
#tpmask {
	background-color: #000000;
	z-index: 9999;
	display: block;
	position: absolute;
	left: 0;
	top: 0;
	opacity: 0.6;
	height: 100%;
	width: 100%;
}
 
#boxes .window {
	right:20px;
	top:20px;
	border-radius: 5px;';
  	-moz-border-radius: 5px;';
  	-webkit-border-radius: 5px;';
	width:auto;
	height:auto;
	display:none;
	z-index:9999;
	padding:20px;
	box-shadow: 0 0 18px rgba(0, 0, 0, 0.4);
}
 
#boxes #dialog {
	position: absolute;"; 
	width: auto;";
	margin: auto;";
	max-width: 800px; 
	height: auto;
	_width: 0;
	white-space: normal;
	overflow: visible;
	padding: 10px;
	font-family: 'Lucida Grande', Arial, 'Arial Unicode MS', Helvetica, sans-serif !important;
	color: #FFFFFF;
	font-size:13px !important;
}
 
#dialog a:link, a:visited, a:hover {
	color: #000000
}
 
*html #boxes .window {
	position: absolute;
}
 
#boxes .window .close {
	background-attachment: scroll;
	background-clip: border-box;
	background-color: transparent;
	background-image: url(<?php echo plugins_url('images/close.png',__FILE__ ); ?> );
	background-origin: padding-box;
	background-position: 0% 0%;
	background-repeat: no-repeat;
	background-size: auto;
	height: 36px;
	right: -19px;
	margin: 0px 0px 0px 0px;
	padding: 0px 0px 0px 0px;
	position: absolute;
	top: -19px;
	width: 36px; 
}
</style>