[BUG] `position-anchor` pointing from the `:host` of a custom element to another element is broken

[jpzwarte]

The following HTML snippet doesn't work correctly with the polyfill:

<button style="anchor-name: --button">Button</button>
<x-tooltip style="position-anchor: --button">
  <!-- more CSS anchor positioning within the shadow root of the custom element -->
</x-tooltip>

You can see some polyfill changes to the CSS of the custom element, but the actual positioning is broken.