#mmc a {
display: block;
margin-left: auto;
margin-right: auto;
margin-top: 10px;
text-align: center;
background: url(web_pics/mmc.png) no-repeat;
height: 27px;
width: 27px;
overflow: hidden;
}

#mmc a:hover {
background-position: -27px 0;
margin-left: auto;
margin-right: auto;
}