The dropdown listbox, optgroup labels, and options should all be part of the CSS box model and have all the styling options available. That would allow full styling (including border, margin, padding, text and background colour) and make the listbox match the other element styling.
That would go a long way, but doesn't support more complex UI like checkboxes in the dropdown (for a compact multiselect component), a treeview instead of a listbox (including checkbox support), and highlighting parts of option text for things like autocomplete (with the ability to filter based on what's being typed).
It would also be useful to know if the listbox is being displayed above or below the select, so with a rounded border, you can style both the select input and listbox to have a flat edge on the top or bottom accordingly.
For checkboxes, it should be possible to theme them more easily, including:
1. border width, colour, and radius for the box;
2. a graphic or unicode character for the checked and mixed states;
3. optionally an image for the entire checkbox.
That would go a long way, but doesn't support more complex UI like checkboxes in the dropdown (for a compact multiselect component), a treeview instead of a listbox (including checkbox support), and highlighting parts of option text for things like autocomplete (with the ability to filter based on what's being typed).
It would also be useful to know if the listbox is being displayed above or below the select, so with a rounded border, you can style both the select input and listbox to have a flat edge on the top or bottom accordingly.
For checkboxes, it should be possible to theme them more easily, including: 1. border width, colour, and radius for the box; 2. a graphic or unicode character for the checked and mixed states; 3. optionally an image for the entire checkbox.