<div></div>

html {
  display: table;
  height: 100%;
  width: 100%;
}

body {
  display: table-cell;
  vertical-align: middle;
}

div {
  margin: auto;
  width: 100px;
  height: 100px;
  outline: inset 100px green;
  outline-offset: -125px;
}