function rand(){
    return Math.round(Math.random()*(css.length-1));
}

var css = new Array(
	'<link rel="stylesheet" type="text/css" href="default.css">',
	'<link rel="stylesheet" type="text/css" href="capra.css">',
	'<link rel="stylesheet" type="text/css" href="farina.css">',
	'<link rel="stylesheet" type="text/css" href="nocciolo.css">',
	'<link rel="stylesheet" type="text/css" href="olio.css">',
	'<link rel="stylesheet" type="text/css" href="spremuta.css">'
);

rand = rand();

document.write(css[rand]);