.responsive-video-vertical {
    position: relative;
    padding-bottom: 177.78%; /* 16:9 aspect ratio is 56.25%, so 9:16 is 177.78% */
    height: 0;
    overflow: hidden;
    max-width: 100%;
}

.responsive-video-vertical iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}