/* This element defines the size the iframe will take.*/
.ratio-1-78 {
  position: relative;
  width: 100%;
  height: 0;
  padding-bottom: 56.25%;
}

/* Adjust the iframe so it's rendered in the outer-width and outer-height of it's parent */
.ratio-1-78 iframe {
  position: absolute;
  width: 100%;
  height: 100%;
  left: 0;
  top: 0;
}