footer {
    position: relative;
    width: 100%;
    padding: calc((2.75em + 42px) / 4) 0;
    bottom: 0;
    left: 0;
    right: 0;
    text-align: center;
    color: #fff;
    background-color: #393939;
    z-index: 2;
}

button.social {
    cursor: pointer;
    outline: none;
    border-radius: 50%;
    width: 36px;
    height: 36px;
    margin: 3px;
    background-color: transparent;
}

button.social#fb {
    background: url('../icons/fb.jpg');
    background-size: cover;
}

button.social#tw {
    background: url('../icons/tw.jpg');
    background-size: cover;
}

button.social#flickr {
    background: url('../icons/flickr.jpg');
    background-size: cover;
    background-color: #fff;
}

button.social#mail {
    background: url('../icons/mail.jpg');
    background-size: cover;
}