-+
      |        |        |        |
   75 |        |        |        |
      |        |        |        |
      +--------+--------+--------+
      |        |        |        |
  175 |        |        |        |
      |        |        |        |
      +--------+--------+--------+

  -->
<style>
  #container {
    position: absolute;
    width: 400px;
    height: 400px;
  }
  #anchored {
    position: absolute;
    align-self: stretch;
    justify-self: stretch;
    position-anchor: --anchor;
  }
  #anchor