.pwg-icon-cast {
    background-image: url("img/ic_media_route_off_holo_light.png");
    background-size:26px;
}

a:hover .pwg-icon-cast {
    background-image: url("img/ic_media_route_off_holo_dark.png");
}

.cast-btn-on:hover .pwg-icon-cast,
.cast-btn-on .pwg-icon-cast {
    background-image: url("img/ic_media_route_on_holo_dark.png");
}