Hello,
You might also consider using jQuery for this as it has a simple plugin which does this as well.
In the following example I used kOverlay:
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Test Document</title>
<script src='https://code.jquery.com/jquery-1.4.2.min.js'></script>
<script src='https://plugins.jquery.com/files/jquery.koverlay.1.3.js.txt'></script>
</head>
<body>
<a href='javascript: void(0);' onclick="
$('#my_hidden_div_id_1').koverlay({title: 'Put Your Title Here or Not'});
$('.css_koverlay').css({'background-color':'#9c183a'});
">
Link Text
</a>
<div id="my_hidden_div_id_1" style="display: none;">
Put your content here...
</div>
</body>
</html>
Abraham