.rect-a {
  rect: 30px 50px #ff0;
}
.rect-b {
  rect: 30px * #ff0;
}
.rect-c {
  rect: * 50px #ff0;
}
.rect-d {
  rect: * * #ff0;
}
.rect-e {
  rect: 30px 50px *;
}