.wp-embed-aspect-16-9 .wp-block-embed__wrapper {
  position: relative;
  width: 100%;
  padding-top: 56.25%; /* 16:9 aspect ratio */
  height: 0;
  overflow: hidden;
}

.wp-embed-aspect-16-9  .wp-block-embed__wrapper iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}