CSS for adaptive video

styles.css

.video {
  /* Get aspect ratio */
  --aspect-ratio: calc(var(--height) / var(--width));
  /* Add units to height */
  --height-with-units: calc(var(--height) * 1px);

  max-width: 100%;

  /* Get minimal of initial height
     or height calculated from window width */
  height: min(calc(100vw * var(--aspect-ratio)), var(--height-with-units));
}