Base Colour: It is the base colour of the scrollbar.
Highlight Colour: When you pull on a scrollbar the highlight colour shows.
Shadow Colour: The shadow basicly outlines the scrollbar.
Arrow Colour: The Arrow is the tiny arrow that you click to scroll the bar.
My advice is to go to the " Create your own " scrollbar and fiddle around with some colours to get a better feel of the names.
Where do I put the code?
You place the style code within the head of your document. ( below example )
Your Page
Does it have to be in the head of my page?
Yes it does have to go into the head of your document.
Is it compatible with all browsers?
No, Some Netscape browsers do not handle Scrollbar colours, But css has a trick!
the hides css from non css and older browsers. So you will not get any errors
from using css on your site.