a.mail{
display:block;
margin:0px auto 0px auto;
width:150px;
height:30px;
text-indent:-9999px;
background-image: url("../img/menu08_mail.jpg"); 
background-position:top;
}
a.mail:hover {
background-image: url("../img/menu08_mail.jpg");
background-position:bottom;
}