I've done some more looking into this and I can get it to work fine via iframes.
I've cut and copied your complete placeholder "replace with html" text into notepad and saved it as excel.htm which I then posted HERE
I then copied most of the content of your page 4 into a new document but omitted your placeholder and placed in a new one with the following "Replace with html" code.
The page now works as expected with all the text visible. Of course it's only a 1 page site so I didn't include your buttons.
I attach the web file. If you preview it it should work.
It may be possible to do it the way you tried but I believe you'd need a <head> placeholder for the head section of the code you were using and another for the body part of the html.
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