Ok, I understand the mentality I'm up against, and I think that's evident to anyone who views this thread.

I don't understand the condescending tone that I'm receiving.
I can see that the site was coded from scratch, and I totally respect that, which is why I gave an approach that barely touched anything.
As I mentioned: any code that didn't know "fullscreen.php (fully able to be implemented in index.php as a function/section) would not be affected: It would simply call the graphic file itself.

I'm not proposing a new structure, nor a massive change, just a little page that is called by one part of one (or 2) function(s).