This can be done in WebKit-based browsers (such as Chrome and Safari) with only CSS:
::-webkit-scrollbar {
width: 2em;
height: 2em
}
::-webkit-scrollbar-button {
background: #ccc
}
::-webkit-scrollbar-track-piece {
background: #888
}
::-webkit-scrollbar-thumb {
background: #eee
}
References: