  width: anchor-size(width);
  height: anchor-size(height);
  background: lime;
  opacity: .3;
}
</style>
<body onload="checkLayoutForAnchorPos('.target')">
  <div class="relpos">
    <div class="spacer" style="height: 10px"></div>
    <div class="columns relpos">
      <div class="spacer" style="height: 40px"></div>
      <div class="relpos">
        <div class="colspan">
          <div class="relpos">
            <!--
              The containing block chain of this anchor is `relpos`, `colspan`,
        