var sfondoOrigWidth;
var sfondoOrigHeight;
$(window).load(
	    function() {
	    	resizeBG();
	    }
	);



$(window).resize(function(){
	resizeBG();

});

function resizeBG(){
	sfondoOrigWidth = eliminatePX($("#sfondo-css").css("width"));
	sfondoOrigHeight = eliminatePX($("#sfondo-css").css("height"));

	$("#sfondo-css").css("width",$(window).width()+"px");
	newH = (eliminatePX($("#sfondo-css").css("width"))*sfondoOrigHeight)/sfondoOrigWidth;
	$("#sfondo-css").css("height",newH);

}

function eliminatePX(valore){

	if(valore){
		return valore.substr(0,(valore.length-2));
	}

}