div {
  background-size: inherit ;
}
div {
  background-size: 0;
}
div {
  background-size: 12em;
}
div {
  background-size: 42px;
}
div {
  background-size: 12%;
}
div {
  background-size: auto;
}
div {
  background-size: 12em auto;
}
div {
  background-size: auto 42%;
}
div {
  background-size: 12px 42%;
}
div {
  background-size: cover;
}
div {
  background-size: contain;
}
div {
  background-size: auto, auto auto, 12px 42%, cover, contain, 12em;
}