<style>
body  {
    background-image: url("http://i.imgur.com/kcmsgdr.png");
    background-color: #cccccc;
}
</style>

#a{
    margin: 3.55cm 5.025cm;
    height: 40px;
    width: 40px;
    content: url(http://i.imgur.com/59fHyah.png);
}
#a:checked {
    content: url(http://i.imgur.com/zgwd1n1.png);
}



#b{
    margin: 3.55cm -0.65cm;
    height: 40px;
    width: 40px;
    content: url(http://i.imgur.com/59fHyah.png);
}
#b:checked {
    content: url(http://i.imgur.com/zgwd1n1.png);
}

#b{
    margin: 3.55cm -0.65cm;
    height: 40px;
    width: 40px;
    content: url(http://i.imgur.com/59fHyah.png);
}
#b:checked {
    content: url(http://i.imgur.com/zgwd1n1.png);
}