everylayout/frame.css

/*===========*/
/* The Frame */
/*===========*/

.frame {
  --n: 9;
  --d: 16;
  padding-bottom: calc(var(--n) / var(--d) * 100%);
  position: relative;
}

.frame > * {
  overflow: hidden;
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  display: flex;
  justify-content: center;
  align-items: center;
}

.frame > img,
.frame > video {
  width: 100%
  height: 100%
  object-fit: cover;
}