black;
  }
  #anchor {
    position: absolute;
    left: 10px;
    top: 10px;
    width: 20px;
    height: 20px;
    background: coral;
    anchor-name: --a;
  }
  #target {
    position: absolute;
    background: skyblue;
    position-anchor: --a;
    left: 9999px; /* force overflow */
    position-try-fallbacks: --pt;
  }
</style>

<div id=cb>
  <div id=anchor></div>
  <div id=target></div>
</div>
<script>
  function assert_unit_value(actual, expected) {
    assert_true(actual instanceof CSSUnitValue);
  