edit.html

<!doctype html>
<html lang=en>
<head>
<meta charset=utf-8>
<title>txt</title>
  <link rel="stylesheet" type="text/css" href="{{ url_for('static', filename='edit.css') }}" />
  <script src="{{ url_for('static', filename='edit.js') }}" type="text/javascript"></script>
</head>
<body>
    <form action="/document.json" method="post">
        <p>
            <label for="content">Content (markdown supported)</label>
            <textarea name="content" autofocus></textarea>
        </p>
        <p><input type="submit" value="save" /></p>
    </form>
</body>
</html>