How to create transparent navigation bar like in new twitter?

I want to add navigation bar at the top side of my web site like in new twitter design. How can I add it? (p开发者_StackOverflow中文版lease see example below...)

There is a div called top-stuff. It has the following css:

#top-stuff {
    left: 0;
    position: fixed;
    top: 0;
    width: 100%;
    z-index: 12;
}