.left {
  display: inline-block;
  width: 45%;
  vertical-align: top;
  overflow: scroll;
}

.right {
  display: inline-block;
  width: 45%;
  aspect-ratio: 10 / 10;
  vertical-align: top;
  overflow: scroll;
}

.right iframe {
  display: inline-block;
  width: 100%;
  height: 100%;
  border: inset;
  overflow: scroll;
}