chromium/third_party/blink/web_tests/inspector-protocol/dom/resources/dom-get-anchor-element.html

<!DOCTYPE html>
<html>
  <style>
    .parent {
      position: relative;
    }

    #named-anchor {
      anchor-name: --anc;
    }

    #default-anchor {
      anchor-name: --default;
    }

    #unreachable-anchor {
      anchor-name: --unreachable;
    }

    #target {
      position: absolute;
    }

    #default-target {
      position-anchor: --default;
      position: absolute;
    }
  </style>
  <body>
    <div class="parent">
      <div id="named-anchor"></div>
      <div id="implicit-anchor"></div>
      <div id="default-anchor"></div>
      <div id="target" anchor="implicit-anchor"></div>
      <div id="default-target"></div>
    </div>
    <div id="unreachable-anchor"></div>
  </body>
</html>