Customize scrollbar with javascript or JQuery

For my items pages, the list of metadata is quite long and I've set an absolute size for the div that holds my metadata, and I added a scrollbar in the style.css file (overflow:auto). I'd like to customize the appearance of my scrollbar. The methods I've found involve CSS, a javascript file, and some coding at the top of the html page.

Where would I put each of these items? My items page is show.php, so where should the coding go that is normally at the top of an html page?

Where should I put the scrollbar.js file, in which folder?

I assume I would just add the CSS for the scrollbar to the style sheet in my theme, is that right?

You're right about the CSS; just put that in your theme's style.css file.

You can put your JavaScript files in a directory called javascripts within your theme. Then, if you're using Omeka 1.3 or later, before the head function (but after <?php) in your theme's show.php file, just add:

queue_js('scrollbar');

Omeka will then add your javascript to your page for that particular view. You can read more about queue_js in the Omeka codex.