function posLightbox(id){
	wDiv = document.getElementById(id).offsetWidth;
	hDiv = document.getElementById(id).offsetHeight;
	document.getElementById(id).style.marginLeft=-(wDiv/2)+'px';
	document.getElementById(id).style.marginTop=-(hDiv/2)+'px';
	if (window.innerHeight){
	   //No IE
   		hscreen = window.innerHeight
		}
		else {
   		if (document.body.clientHeight){
      	//Old IE
	   hscreen = document.body.clientHeight
   		}
	}
	if (hscreen<hDiv){
		document.getElementById(id).style.top='20px';
		document.getElementById(id).style.marginTop='0';
		document.getElementById(id).style.position='absolute';
	}
	else
		document.getElementById(id).style.position='fixed';
}
function openLightbox(id) {
    document.getElementById(id).style.display='block';
	document.getElementById('overlay').style.display='block';
	posLightbox(id);
}
function closeLightbox(id) {
    document.getElementById(id).style.display='none';
	document.getElementById('overlay').style.display='none';
}