Customizable select listbox

### MDN URL

https://developer.mozilla.org/en-US/docs/Learn_web_development/Extensions/Forms/Customizable_select

### What specific section or headline is this issue about?

_No response_

### What information was incorrect, unhelpful, or incomplete?

I am working on supporting the listbox rendering mode for customizable select, which allows `appearance:base-select` to work on `` and ``. This will be shipping somewhat soon in chrome.
- https://github.com/whatwg/html/pull/11758
- https://chromestatus.com/feature/6222145025867776

This does not make `appearance:base-select` work on multi-select with a dropdown, which you get by doing ``. That will be worked on as a follow up.

### What did you expect to see?

This should be documented in the customizable select article, and possibly the main select element page if applicable.

### Do you have any supporting links, references, or citations?

_No response_

### Do you have anything more you want to share?

_No response_