当height为100%时，如何保持纵横比？

.container {
  width: 100%;
  aspect-ratio: 16/9; /* 16:9纵横比 */
}

.container {
  width: 100%;
  position: relative;
}

.container::before {
  content: "";
  display: block;
  padding-top: 56.25%; /* 16:9纵横比 */
}

.container > .content {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

<div id="container"></div>

<script>
  window.addEventListener('resize', function() {
    var container = document.getElementById('container');
    var width = container.offsetWidth;
    var height = width * 9 / 16; /* 16:9纵横比 */
    container.style.height = height + 'px';
  });
</script>