function centerDialogBox()
	{
	var dialog_background = document.getElementById("dialog_background");
	var dialog_content = document.getElementById('dialog_content');
	var window_width = (window.innerWidth ? window.innerWidth : document.body.offsetWidth);
	var window_height = (window.innerHeight ? window.innerHeight : document.body.offsetHeight);
	var dialog_width = dialog_content.clientWidth;
	var dialog_height = dialog_content.clientHeight;
	var dialog_left = parseInt((window_width - dialog_width) / 2);
	if(dialog_left < 0)
		{ 
		dialog_left = 0; 
		}
	var dialog_top = parseInt((window_height - dialog_height) / 2);
	if(dialog_top < 0)
		{ 
		dialog_top = 0; 
		}
	dialog_background.style.width = window_width + 'px';
	dialog_background.style.height = window_height + 'px';
	dialog_content.style.left = dialog_left + 'px';
	dialog_content.style.top = dialog_top + 'px';	
	}

function openDialogBox()
	{
	var dialog_background = document.getElementById("dialog_background");
	var dialog_content = document.getElementById('dialog_content');
	dialog_background.style.display = 'block';
	dialog_content.style.display = 'block';
	centerDialogBox();
	window.onresize = centerDialogBox;
	}
	
function closeDialogBox()
	{
	var dialog_background = document.getElementById('dialog_background');
	var dialog_content = document.getElementById('dialog_content');
	dialog_background.style.display = 'none';
	dialog_content.style.display = 'none';	
	}