.foo {
  position: absolute;
  top: 10px;
  right: 20px;
  bottom: 30px;
  left: 40px;
}

.bar {
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
}

.baz {
  position: absolute;
  top: 30px;
  right: auto;
  bottom: 30px;
  left: auto;
}

.fab {
  position: relative;
  top: 50%;
  right: 0;
  bottom: 20px;
  left: 0;
}