So here is what I would do if I were you:
The following would be https://mydomainame.com/flight.php or flight depending on your htaccess.
You a button would now be:
<a class="book-flight-btn" href="https://mydomainame.com/flight>Book flight</a>
in flight.php You would have this code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Test Layout</title>
<style type="text/css">
body, html
{
margin: 0; padding: 0; height: 100%; overflow: hidden;
}
#content
{
position:absolute; left: 0; right: 0; bottom: 0; top: 0px;
}
</style>
</head>
<body>
<div id="content">
<iframe width="100%" height="100%" frameborder="0" src="https://fairdealtravel.tripprosites.com/" />
</div>
</body>
</html>
The previous html code is what is recommended by this question: Full Page <iframe>
Does this make sense?