Base appearance for list box select elements

[josepharhar]

What is the issue with the HTML Standard?

In the customizable select PR, we defined base appearance for the select element rendered as a drop-down box without the multiple attribute.

Next, I’d like to define base appearance for the select element when rendered as a list box, with and without the multiple attribute.

Relevant HTML issues:

• Rendering <select> as a listbox is a one-line widget that opens a popup on iOS and Android #8189

Relevant CSS issues:

• [css-forms-1] Should appearance: base-select work on listbox selects? (<select size>/<select multiple>) w3c/csswg-drafts#12468
• [selectors] Add pseudo-classes for <select> being a drop-down box vs a list box w3c/csswg-drafts#7422
• [css-forms-1] UA styles for base appearance listbox select elements w3c/csswg-drafts#12510