function gcOverlay(mode) {
	if(mode == 'display') {
		if(document.getElementById("gcOverlay") === null) {
			div = document.createElement("div");
			div.setAttribute('id', 'gcOverlay');
			div.setAttribute('className', 'gcOverlayBG');
			div.setAttribute('class', 'gcOverlayBG');


			lightBox = document.createElement('div');
			lightBox.setAttribute('id', 'gcLightBox');

			span = document.createElement('span');
			span.setAttribute('class', 'closeButton');
			span.setAttribute('className', 'closeButton');
			span.setAttribute('onclick', 'gcOverlay(\'none\')');
			text = document.createTextNode('Hier klicken zum Schließen');
			span.appendChild(text);
			lightBox.appendChild(span);
			
			iframe = document.createElement('iframe');
			iframe.setAttribute('width', '780');
			iframe.setAttribute('height', '600');
			iframe.setAttribute('frameborder', 'no');
			iframe.setAttribute('src', './gc/restylegc.php?showTitle=0&height=500&wkst=2&hl=de&bgcolor=%23FFFFFF&src=4i0poqr0q5umj1dqhpvav50r40@group.calendar.google.com&color=%23A32929&src=mtojen41m54fskr6hp6tiobofc@group.calendar.google.com&color=%237A367A&src=52cpgraj425kl3gout2djt3u5g@group.calendar.google.com&color=%232952A3&src=vc5iuq9vr1drkir58r8ppq6kro@group.calendar.google.com&color=%230D7813&src=dp8fogp3en3vp7ui47hqjupufo@group.calendar.google.com&color=%235A6986&ctz=Europe/Berlin&gsessionid=OK');
			
			lightBox.appendChild(iframe);

			document.getElementsByTagName("body")[0].appendChild(div);
			document.getElementsByTagName("body")[0].appendChild(lightBox);
		}
	} else {
		document.getElementsByTagName("body")[0].removeChild(document.getElementById("gcOverlay"));
		document.getElementsByTagName("body")[0].removeChild(document.getElementById("gcLightBox"));
	}
}