// by id
function changeClass(el,cl)
{
	var e = document.getElementById(el);
	if(e){
		e.className = cl;
	}
}

function switchBackground(background){
	if(background){
		var x = document.getElementsByTagName('body')[0];
		if(x){
			x.style.backgroundImage = "url(../images/background_"+background+".jpg)";
		}
	}
}