<!DOCTYPE html>
<html>
<head>
    <style>
        body, html {
            height: 100%;
            margin: 0;
            position: fixed;
            top: -200px;
        }
        .section {
            height: 2000px;
        }
        .overlay {
            position: fixed;
            left: 0;
            top: 0;
            width: 400px;
            height: 100px;
            background-color: blue;
        }
    </style>
</head>
<body>
    <div class="section"></div>
    <div class="overlay"></div>
</body>
</html>