.field input.youtube {
    background-image: url('../images/field-video-youtube.png');
    background-position: 6px center;
    background-repeat: no-repeat;
    background-size: 28px 20px;
    padding-left: 40px;
}

.field input.youku {
    background-image: url('../images/field-video-youku.png');
    background-position: 6px center;
    background-repeat: no-repeat;
    background-size: 28px 20px;
    padding-left: 40px;
}