Scroll particular DIV contents with browser’s main scrollbar

Though your Gizmodo example uses additional scripts for handling of (the vertical scroll bar of) the sidebar (which even doesn’t work in all browsers), the effect is perfectly possible with pure CSS and it even is not as difficult as it may seem at first sight.

So you want:

• A horizontally centered layout, possibly widened or narrowed for different browser window sizes,
• The main content at the left which is vertically scrollable by the browser’s main scroll bar,
• A sidebar at the right which sticks to the top of the browser window, scrollable separately from the main content, and only showing its scroll bar when the mouse hovers over. When scrolled to the end of the sidebar, the window’s scroll bar takes over.

See this demonstration fiddle which does all that.

The style sheet:

html, body, * {
    padding: 0;
    margin: 0;
}
.wrapper {
    min-width: 500px;
    max-width: 700px;
    margin: 0 auto;
}
#content {
    margin-right: 260px;  /* = sidebar width + some white space */
}
#overlay {
    position: fixed;
    top: 0;
    width: 100%;
    height: 100%;
}
#overlay .wrapper {
    height: 100%;
}
#sidebar {
    width: 250px;
    float: right;
    max-height: 100%;
}
#sidebar:hover {
    overflow-y: auto;
}
#sidebar>* {
    max-width: 225px; /* leave some space for vertical scrollbar */
}

And the markup:

<div class="wrapper">
    <div id="content">
    </div>
</div>
<div id="overlay">
    <div class="wrapper">
        <div id="sidebar">
        </div>
    </div>
</div>

Tested on Win7 in IE7, IE8, IE9, Opera 11.50, Safari 5.0.5, FF 5.0, Chrome 12.0.

I assumed a fluid width for the main content and a static width for the sidebar, but both can perfectly be fluid, as you like. If you want a static width, then see this demo fiddle which makes the markup more simple.

Update

If I understand your comment correctly, then you want to prevent scrolling of the main content when the mouse is over the sidebar. For that, the sidebar may not be a child of the scrolling container of the main content (which was the browser window), to prevent the scroll event from bubbling up to its parent.

I think this new demo fiddle does what you want:

<div id="wrapper">
    <div id="content">
    </div>
</div>
<div id="sidebar">
</div>