.responsive-video-container {
    position: relative;
    margin-bottom: 1em;
    padding-bottom: 56.25%;
    height: 0;
    overflow: hidden;
    max-width: 100%;
}
.responsive-video-container iframe{
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}