function openPopup() {
	var body = document.body.offsetHeight;
	var center_hor = document.getElementById("center_hor").offsetHeight;
	
	document.getElementById('popup_overlay').style.height = center_hor + 10 + "px";
	
	reposPopup();
	
	document.getElementById('popup_overlay').style.display = "block";
	document.getElementById('popup_div').style.display = "block";
}

function popupClose() {
	document.getElementById('popup_overlay').style.display = "none";
	document.getElementById('popup_div').style.display = "none";
}

function reposPopup() {
	
	// repos the popup
	if(self.pageYOffset) {
		var scrollOffset = self.pageYOffset;
	} else if(document.documentElement) {
		var scrollOffset = document.documentElement.scrollTop;
	} else if(document.body) {
		var scrollOffset = document.body.scrollTop;
	}
	
	if(scrollOffset) {
		var popupObj = $("popup_div");
			popupObj.style.top = scrollOffset + "px";
	}
}