Fixed positioned div within a relative parent div

Question

This question came first on Google although an old one so I’m posting the working answer I found, which can be of use to someone else.

This requires 3 divs including the fixed div.

HTML

<div class="wrapper">
    <div class="parent">
        <div class="child"></div>
    </div>
</div>

CSS

.wrapper { position:relative; width:1280px; }
    .parent { position:absolute; }
        .child { position:fixed; width:960px; }