The answer is
For the sake of completeness, what you are trying to create is a "modal window".
Numerous JS solutions allow you to create them with ease, take the time to find the one which best suits your needs.
I have used Tinybox 2 for small projects : http://sandbox.scriptiny.com/tinybox2/
You can simply use jQuery UI Dialog
Example:
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$(function() {_x000D_
$("#dialog").dialog();_x000D_
});<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>_x000D_
<html lang="en">_x000D_
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<head>_x000D_
<meta charset="utf-8" />_x000D_
<title>jQuery UI Dialog - Default functionality</title>_x000D_
<link rel="stylesheet" href="http://code.jquery.com/ui/1.10.3/themes/smoothness/jquery-ui.css" />_x000D_
<script src="http://code.jquery.com/ui/1.10.3/jquery-ui.js"></script>_x000D_
<link rel="stylesheet" href="/resources/demos/style.css" />_x000D_
</head>_x000D_
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<body>_x000D_
<div id="dialog" title="Basic dialog">_x000D_
<p>This is the default dialog which is useful for displaying information. The dialog window can be moved, resized and closed with the 'x' icon.</p>_x000D_
</div>_x000D_
</body>_x000D_
</html>Source: Stackoverflow.com