From 2007.igem.org

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.rollover a {
display: block;
height: 479px;
width: 480px;
padding:10px 10px 10px 7px;
font: bold 13px sans-serif;;
color:#333;
background: url("https://static.igem.org/mediawiki/2007/2/21/Rollover_adelman.png") 0 0 no-repeat;
text-decoration: none;
}
.rollover a:hover { 
background-position: -500px 0;
color: #049;
}