function Mostra(testo)
{
livello.innerHTML = testo;
livello.style.visibility = "Visible";
livello.style.position = "Absolute";
livello.style.left = event.clientX - 300;
livello.style.top = event.clientY - 50;
}
function Nascondi()
{
livello.style.visibility = "Hidden";
}