Custom Webkit Scrollbars
Customized scrollbars only supported in Webkit Browsers. As you can see, the scrollbars have been customized with vendor prefixed CSS properties (pseudo classes) like
::-webkit-scrollbar, etc. It looks a lot nicer than the default scrollbars in my opinion.
There's an excellent tutorial on CSS Tricks that will teach you how to customize scrollbars in webkit based browsers from scratch.