SO chat: how to make the sidebar not respond to scroll event?

I am using chat feature of chat.stackoverflow.com... It's really amazing! I am curious, when I scroll the window, the right side of the chat room(div id="sidebar") didn't respond to the scroll event at all, how that can be 开发者_如何学运维achieved?

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Fixed positioning.

#sidebar {
    height: 100%;
    position: fixed;
    right: 0px;
    top: 0px;
    width: 28%;
}