Add the following to your .css file, and play with the hexadecimal colour values:
body {
scrollbar-face-color: #8080FF;
scrollbar-arrow-color: #FFFFFF;
scrollbar-track-color: #DDDDFF;
scrollbar-shadow-color: '';
scrollbar-highlight-color: '';
scrollbar-3dlight-color: '';
scrollbar-darkshadow-Color: '';
}