Customizable select multiple dropdown

[josepharhar]

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?

We are implementing base appearance for the last mode of the select element, the multiple drop down: <select multiple size=1>

• Define base appearance for select multiple drop-down whatwg/html#12069
• https://chromestatus.com/feature/5070067395067904

Here is a basic example:

<select multiple size=1>
  <option>one</option>
  <option>two</option>
</select>
<style>
select, ::picker(select) {
  appearance: base-select;
}
</style>

Base appearance for single-select dropdown was already documented here: #37857

Base appearance for single and multi-select listboxes is tracked here: #42358

Related issue about mobile/desktop parity: #43403

What did you expect to see?

Documentation about using appearance:base-select on <select multiple size=1>

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

No response

Do you have anything more you want to share?

I mentioned in the mobile/desktop parity issue that the spec was written such that <select multiple size=1> may be rendered as either a listbox or dropdown in some browsers. However, with the way discussions have been going so far, putting appearance:base-select on <select multiple size=1> is supposed to guarantee that it will be a drop-down box.