multi-select styling

[planktonic]

The styling of select[multiple] is pretty odd, as it gets the down-arrow and hover styles of a normal select. Even though these aren’t normally used, it’d be great to avoid breaking them. Some first suggestions:

• Add a story
• scope the down-arrow styling to non-multi selects
• hover/focus styling should be applied to the options, not the whole select
• … anything else that looks a bit broken