Background-attachment:fixed откуда высчитывает начало?

* {
  margin: 0;
  padding: 0;
}

html,
body {
  position: relative;
  height: 50vh;
  width: 90vw;
  left: 50px;
  top: 50px;
  background-color: red;
}

body {
  left: 100px;
  top: 100px;
  background-color: green;
}

div {
  position: absolute;
  width: 90%;
  height: 40vh;
  left: 50px;
  top: 50px;
  background-color: orange;
  background-image: url(https://avatars.mds.yandex.net/get-pdb/1636783/96989b87-2116-4678-a8ee-ae113469504d/s1200?webp=false);
  background-attachment: fixed;
  background-position: 205px 205px;
  background-repeat: no-repeat;
}

<div></div>