Provide a data-attribute that exposes the final anchor-direction

[ta834n]

Hi folks,

I like the headlessui-library a lot and I regularly use it in a project I am working for.

In that particular project the designers designed a Listbox-component that looks differently depending on the direction it is opened.
The closed Listbox has rounded corners but the opened Listbox has only rounded corners on the opposite side of the ListboxOptions.
I attached a simple drawing to make that clear:

The problem is that I can specify an anchor-property with the ListboxOptions-component but the ListboxButton-component needs to know the direction the ListboxOptions are actually rendered.

I found out that the ListboxOptions-component exposes an (undocumented?) attribute data-anchor from which I could deduce the direction.
But I do not know how to use that attribute in my ListboxButton-component.

Since the ListboxOptions are rendered to a portal I cannot use the peer: -pseudo selector because ListboxOptions and ListboxButton are no siblings in the DOM.

Could you please tell me how I could implement the given design requirements?

Thank you very much in advance.