function getCSS()
{
datetoday = new Date();
timenow=datetoday.getTime();
datetoday.setTime(timenow);
thehour = datetoday.getHours();

if (thehour < 7)
 document.body.className="noche";
else if (thehour >= 7 && thehour < 9)
 document.body.className="amanecer";
else if (thehour >= 9 && thehour < 19)
 document.body.className="dia";
else if (thehour >= 19 && thehour < 22)
 document.body.className="atardecer";
else if (thehour >= 22 && thehour <= 24)
 document.body.className="noche";
else
 document.body.className="default";
}