<!DOCTYPE html>
<html>
<head>
    <meta name='viewport' content='width=device-width, initial-scale=1'>
    <style>
        body {
            margin: 0;
            width: 100%;
            height: 10000px;
        }
        #nav {
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            height: 50px;
            background-color: black;
        }
    </style>
</head>
<body>
    <div id="nav"></div>
</body>
</html>