Relevant JSFiddle - http://jsfiddle.net/Efqda/
CSS -
.social img {
    width: 128px;
    height: 128px;
    opacity: .5;
}
.social img:hover {
    opacity: 1.0;
}
.social #facebook img {
    content: "https://raw.github.com/danleech/simple-icons/master/icons/facebook/facebook-128-black.png";
}
HTML -
<a href="facebook.com"><img class="social" id="facebook"></a>
How do I get the image to show up? I don't get any errors in the console.
 
     
     
     
     
     
     
     
    