I guess first thing to say is why not use the template system rather than hard coding the html into the file.
put below
eval('$navbar = "' . fetch_template('navbar') . '";');
something like
eval('print_output("' . fetch_template('challenge_template') . '");');
then create a template called challenge_template and put inside it something like the following editing it along the way of course.
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Oh i havent actually tested or used this hack at all btw I just took a quick look to see if i could help you out with the header as requested.
hope this helps and good luck