Quando posti del codice devi usare l'apposito tag come facciamo tutti
codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Documento senza titolo</title>
<style type="text/css">
<!--
.style3 a:hover {
	width: 100px;
	height: 100px;
	display: block;
	color: transparent;
	background: url(mappa.jpg) no-repeat;
}
-->
</style>
</head>

<body>
<p class="style3">dove siamo</p>
</body>
</html>