Jquery 使div永久居中_屏幕改变大小仍然居中实例

<script type="text/javascript" src="js/jquery-1.9.1.js"></script>
<script type="text/javascript">
$(function()
{
var w = 400;
var h = 50;
$("#top").css("border","solid black 1px");
$("#top").css("color","red");
$("#top").css("position","absolute");
$("#top").css("width",w).css("height",h);

var x = ($(window).width()-w)/2;
var y = ($(window).height()-h)/2;
$("#top").css("top",y).css("left",x);
alert("x"+x+",y"+y);
$("#top").attr("align","center");

});
</script>

$("#top").css("top",y).css("left",x);

$("#top").css("margin","0 auto");