<html>
<head>
<style>

body {
    height:2000px;
    margin:0;
    overflow:hidden;
}

#fixed-background-box {
    position: absolute;
    top: -100px;
    width:400px;
    height:600px;
    background-image: linear-gradient(blue, blue 10px, green 10px, green 490px, black 490px, black);
    background-attachment:fixed;
    background-repeat:no-repeat;
}

</style>
<script>
function runTest() {
    if (window.internals)
        window.internals.setTopContentInset(100);
}
window.addEventListener('load', runTest, false);
</script>
</head>
<body>
    <div id="fixed-background-box"></div>
</body>
</html>