Use full width excluding overflow scrollbar with “position: absolute”

I would like to have a small red div with full width at a fixed top position, inside another div that has overflow: scroll. I hope the jsFiddle makes it clear: http://jsfiddle.net/mCYLm/2/.

The issue is that the red div is overlapping the scrollbar. I guess right: 0 means the right hand side of div.wrapper; it does not subtract the scrollbar of div.main. When I move the overflow: scroll into div.wrapper, then the red banner has the right size (fiddle). However, it is not at a fixed position anymore (scrolling down makes the banner scroll up).

How can I achieve the following two things together?

The red banner is at the fixed position like in this fiddle.
The red banner has full width except the scrollbar like in this fiddle.

I'd like to get this working in Google Chrome.

HTML:

<div class="wrapper">
    <div class="red-banner"></div>
    <div class="main">
        <div class="item">foo</div>
        <div class="item">foo</div>
        <div class="item">foo</div>
        <div class="item">foo</div>
    </div>
</div>

CSS:

div.wrapper {
    position: relative;
}

div.main {
    height: 200px;
    overflow-y: scroll;
}

div.item {
    border: 1px solid black;
    margin: 20px;
    padding: 20px;
}

div.red-banner {
    background-color: red;
    position: absolute;
    left: 0;
    top: 0;
    right: 0;
    height: 20px;
}

Seems like this isn't possible with pure CSS, so here's a JavaScript (jQuery) hack:

$(function() {
  var $container = $("<div>").css({ height: 1, overflow: "scroll" }).appendTo("body");
  var $child = $("<div>").css({ height: 2 }).appendTo($container);
  window.SCROLLBAR_WIDTH = $container.width() - $child.width();
  $container.remove();
});

then:

$("div.red-banner").css({
  right: SCROLLBAR_WIDTH
});

HTML

<div class="scroller">
    <div class="banner-wrapper">
        <div class="banner"></div>
    </div>
</div>

<div class="main">
    <div class="item">foo</div>
    <div class="item">foo</div>
    <div class="item">foo</div>
    <div class="item">foo</div>
</div>

CSS

* { margin: 0; padding: 0 }
body {
    padding-top: 30px;
}

div.main {
    height: 200px;
    width: 100%;
    overflow-y: scroll;
    position: absolute;
    z-index: 50;
    background: -webkit-gradient(linear, center top, center bottom, from(white), to(rgba(255,255,255,0)));
}

div.item {
    border: 1px solid black;
    margin: 20px;
    padding: 20px;
}

div.scroller {
    height: 20px;
    width: 100%;
    position: absolute;
    z-index: 100;
    overflow: hidden;
}

div.banner-wrapper {
    background: transparent;
    position: relative;
    height: 20px;
    overflow-y: scroll;
    left: 0;
    margin-right: -20px;
}
div.banner {
    height: 20px;
    background: -webkit-gradient(linear, center top, center bottom, from(white), to(rgba(255,255,255,0)));;
    margin-left: 20px;
    margin-right: 40px;
}

Development version: http://jsfiddle.net/mCYLm/13/
Final version: http://jsfiddle.net/mCYLm/14/

Works with zooming and variable viewport width.
! BUG: Scrollbar button from the right top is not accessable/clickable.

Tested in: