.youtubeBlockResponsive16by9 {
    position: relative;
    height: 0;
    margin-bottom: .5rem;
}
.youtubeBlockResponsive16by9 iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: none;
}

.youtubeBlockResponsive16by9 {
    padding-bottom: 56.25%
}