Troubleshooting Frame 12's Publish pod

[Theresa de Valence]

My unstructured Frame book autonumbers correctly, generates TOC, saves 
to pdf and displays correctly.

I’ve minor experience creating html newsletters, so I’ve seen a CSS. I 
understand enough about ePub to know that a CSS will control formatting.

Using Frame 12’s Publish feature, the ePub is generated successfully. 
The epub has
-chapters out of order,
-a correct TOC (from fm book files), but an error message when Table of 
Contents item is clicked on ("The file x.htm does not exist") [from 
Sigil, an ebook publisher, which shows the content of epubs]
-a CSS for every file in the book

Previously I thought that the left hand (Frame) didn’t know what the 
right (CSS) was doing, or how elements related to each other, and so I 
needed to use a structured Frame document to establish the relationship. 
I’ve been told that’s incorrect.

I now understand that Frame 12’s ability to publish to epub, etc. is 
derived from Robohelp, but it’s been a trillion years since I used 
Robohelp, so that doesn’t help me. I haven’t had a copy of Robohelp on 
my machine for decades, so I can’t see this live.

In the Publish pod, edit Settings, a Style Mapping dialogue shows all of 
the current document’s paragraph tags. Selecting one paratag (the left 
hand) displays a choice of "output" (the right hand). (I posted the 
screen images to adobe.com forum here: 
https://forums.adobe.com/message/6715414#6715414 )

Where does this list of output styles (elements) come from? Adobe’s 
programmers? An accident of fate? What defines what that format is? Is 
this where the CSS comes from?

Since I’m publishing rubbish, have I inadvertently massaged my Settings 
file? Where do I find an uncorrupted one?

I can understand tweaking a CSS to make it better, but I can’t 
understand if I haven’t created a CSS in the first place.

Ideas or pointers are appreciated.

Thanks,
Theresa