.responsive-media {
  position: relative;
  padding-bottom: 56.25%;
  width: 100%;
  height:100%;
  iframe {
    width:100%;
    height:100%;
    position: absolute;
    top: 50%;
    left: 0;
    right: 0;
    bottom: 0;
    margin: 0 auto;
    transform: translateY(-50%);  
  }
}