darken_bg = function( state ) {
	var sfEl = document.getElementById("darkBG");
	var divVideo = document.getElementById("videoframe");
	
	if (state=='on') {
		sfEl.style.display = 'block';
		if (divVideo) {
			divVideo.style.visibility = 'hidden';
		}
	} else {
		sfEl.style.display = 'none';
		if (divVideo) {
			divVideo.style.visibility = 'visible';
		}
	}
}