You can style scrollbars to a degree in both webkit browsers and IE, for Firefox no such CSS exists however so you will need to resort to using a Javascript plugin
Webkit CSS Properties
::-webkit-scrollbar
::-webkit-scrollbar-button
::-webkit-scrollbar-track
::-webkit-scrollbar-track-piece
::-webkit-scrollbar-thumb
::-webkit-scrollbar-corner
::-webkit-resizer
Internet Explorer CSS Properties
scrollbar-face-color
scrollbar-shadow-color
scrollbar-highlight-color
scrollbar-3dlight-color
scrollbar-darkshadow-color
scrollbar-track-color
scrollbar-arrow-color