Coriolan161,
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<style>
#but {
width: 40px;
height: 40px;
background: url("http://icons.iconarchive.com/icons/mazenl77/I-like-buttons-3a/512/Cute-Ball-Go-icon.png") no-repeat;
background-size: 40px 40px;
cursor: pointer;
}
#but:hover {
background: url("http://i.stack.imgur.com/vfLae.png") no-repeat;
background-size: 40px 40px;
}
</style>
</head>
<body>
<div id="but"> </div>
</body>
</html>