With the most latest updates Google has been rolling out, the sites have all been getting custom JS scroll bars (at least in Chrome).
What I like most about it is th
I have been using the lion bars jquery scroller, and I think it meets all the specifications you mentioned, give it a try.
They're done by styling ::-webkit-scrollbar psudo-elements with CSS, not JS.
Take a look at https://gist.github.com/fanzeyi/3995618
Works fine for me.