modal pop up window to fit within browser view if

I've went to this tutorial to do a modal pop up window, and it seems pretty nice for what I need to do. However, I was wondering if someone can help me figure out what I need to calculate to change the dialog box so it'll follow whenever you resize the browser. This tutorial is good because if you resize the browser (width-wise), the box will follow and go into the middle. But if it is height-wise, it wont.

Tutorial : Here

I'm thinking it has to do with these codes :

    // get the screen height and width  
var maskHeight = $(document).height();  
var maskWidth = $(window).width();

// calculate the values for center alignment
var dialogTop =  (maskHeight/3) - ($('#dialog-box').height()/3);  
var dialogLeft = (maskWidth/2) - ($('#dialog-box').width()/2); 

// assign values to the overlay and dialog box
$('#dialog-overlay').css({height:maskHeight, width:maskWidth}).show();
$('#dialog-box').css({top:dialogTop, left:dialogLeft}).show();

I've tried to use $(window).height() but I don't think that works either. I tried to mimic the width styles because that one works, but it doesn't seem to work with height? Can someone help me with this?

Thank you!

Try this

Working demo. You can resize the window and try it re positions the dialog box automatically into center.

$(function(){
    $(window).resize(function(){
    // get the screen height and width  
    var maskHeight = $(window).height();  
    var maskWidth = $(window).width();

    // calculate the values for center alignment
    var dialogTop =  (maskHeight  - $('#dialog-box').height())/2;  
    var dialogLeft = (maskWidth - $('#dialog-box').width())/2; 

    // assign values to the overlay and dialog box
    $('#dialog-overlay').css({ height:$(document).height(), width:$(document).width() }).show();
    $('#dialog-box').css({ top: dialogTop, left: dialogLeft, position:"fixed"}).show();
    }).resize();
});