<html>
<head>
    <style>
        #TB_window
        {
            border: 1px solid red;
            position: fixed;
            top: 0;
            left: 0;
        }
        
        #TB_overlay {
            height: 200px;
            left: 10px;
            position: fixed;
            top: 80px;
            width: 200px;
            
            opacity: 0.1;

            background-color: green;
        }
    </style>
</head>
<body>
    SOME CONTENT
    <div id="TB_overlay">
    </div>
    <div id="TB_window"></div>

</body>
</html>