.ds-backdrop{
  --ds-backdrop-rgb:   23 23 23;
  --ds-backdrop-alpha: .30;
  --ds-backdrop-size:  100% auto;
  --ds-backdrop-veil:  rgb(var(--ds-backdrop-rgb) / calc(1 - var(--ds-backdrop-alpha)));

  background-color: rgb(var(--ds-backdrop-rgb));

  background-image:
    linear-gradient(var(--ds-backdrop-veil), var(--ds-backdrop-veil)),
    url("../img/backdrop-tile.jpg");

  background-image:
    linear-gradient(var(--ds-backdrop-veil), var(--ds-backdrop-veil)),
    image-set(url("../img/backdrop-tile.avif") type("image/avif"),
              url("../img/backdrop-tile.jpg")  type("image/jpeg"));

  background-size:     auto, var(--ds-backdrop-size);
  background-position: 0 0, left top;
  background-repeat:   repeat, repeat-y;
  background-attachment: scroll, scroll;
}