body {
  height: 100vh;
  width: 100%;
  margin: 0;
  background-repeat: no-repeat;
  background-image: url("https://assets.codepen.io/t-90/dog.jpg");
  background-image: image-set(
    "https://assets.codepen.io/t-90/dog.avif" type("image/avif"),
    "https://assets.codepen.io/t-90/dog.webp" type("image/webp"),
    "https://assets.codepen.io/t-90/dog.jpg" type("image/jpg")
  );
  background-size: contain;
  background-position: center;
}