//additional properties for jQuery object
$(document).ready(function(){
//align element in the middle of the screen
$.fn.alignCenter = function() {
//get margin left
var marginLeft = Math.max(40, parseInt($(window).width()/2 - $(this).width()/2)) + 'px';
//get margin top
var marginTop = Math.max(40, parseInt($(window).height()/2 - $(this).height()/2)) + 'px';
//return updated element
return $(this).css({'margin-left':marginLeft, 'margin-top':marginTop});
};

});