video,
img {
  width: 100%;
  height: 100%;
  -o-object-fit: contain;
     object-fit: contain;
}
iframe {
  width: 100%;
  height: 100%;
}
div.center > div {
  display: -webkit-box;
  display: flex;
  -webkit-box-pack: center;
          justify-content: center;
  -webkit-box-align: center;
          align-items: center;
}