posted 12 years ago
You are limited here by the characteristics of the HTML SELECT control, which is in turn defined by the user's browser and OS. A common implementation of this control would put a flat triangle (arrow) at the bottom of the dropdown box for scrolling. Or at the top, as needed. An actual scrollbar is less common.
Speaking as a user, I find any dropdown list with 20 or more elements in it to be awkward, so I recommend meditating on whether this is the optimal way to present your selections.
If you want to ensure an actual scroll bar, you could simply do it the hard way: wrap the list up as a table in a scrollable pop-up div and attach logic/css for highlighting and selection as needed.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.