.rc_fbshareaddon_button {
    background-image:url('../img/facebook.png') !important;
}

.rc_gpshareaddon_button {
    background-image:url('../img/gplus.png') !important;
}

.rc_twittershareaddon_button {
    background-image:url('../img/twitter.png') !important;
}

.rc_tumblrshareaddon_button {
    background-image:url('../img/tumblr.png') !important;
}