background: red;
  font-size: 10px;
  /* stacking  of outlines is undefined, so we cannot reliably to have an outline hide another outline.
   We are using a border instead,
   but still need to create an (invisible) outline to make sure that outline-width does not compute to 0. */
  outline: solid 1em transparent;
  border: solid 1em red;
  margin-left: -10px;
  margin-top: -10px;
}
div > div {
  width: 100px;
  height: 100px;
  background: green;
  font-size: 5px;
  outline-width: inherit;
  outline-style