//HTML
<a href="https://www.facebook.com/" id='facebook-button"></a>


//CSS
#facebook-button a{
	background-image: url("http://i.imgur.com/VBam6AY.png");
	background-color: transparent;
	padding: 0px 0px 0px;
}

#facebook-button a:hover{
	background-image: url("http://i.imgur.com/LEmtZK3.png");
	background-color: transparent;
	padding: 0px 0px 0px;

}