In the CS6 EPUB Export dialog box, on the Advanced Panel > CSS Options, try unchecking Include Style Definitions, Preserve Local Overrides and Include Embeddable Fonts. Then select your own CSS file.
I would guess that the reason it appears to work is because the classes are ignored.
Thanks for the reply.
I meant to mention that I'm exporting with all of those options unchecked...
It seems to happen with HTML export as well. If I create a new file and create a single text box filled with placeholder text and then export it as HTML with all of the CSS options turned off (Include style definitions, Preserve local overrides, and Include fonts) and tell it to use an existing CSS file it -still- includes a second CSS file created by InDesign.
Unless I'm missing something it seems to be impossible to get InDesign to export using an external CSS file and -only- an external CSS file, without trying to add extra code to match some elements of the page layout. This should really be available as an option, shouldn't it? What's the point of writing your own CSS if it's always appended?
Ron Bilodeau who creates EPUB files for O'Reilly wrote a piece about EPUB from CS6 in the newest issue of InDesign Magazine. Perhaps what he says will be useful to you:
"In the Advanced tab of the EPUB Export Options dialog box there is now an option
to include multiple CSS stylesheets, in addition to the CSS that InDesign generates (Figure 3).
"Initially, I was annoyed by this change, because Adobe removed the option to ignore the InDesign-generated CSS and only use a custom external CSS. I write my own custom EPUB CSS and therefore wanted to use that instead of what InDesign generates. But it didn’t take me long to realize that this new solution is pretty elegant. By default, any custom stylesheet attributes will override matching elements from the InDesign-generated CSS. This means that you have ultimate control over what is displayed. If you’re happy with how some of the InDesign-generated CSS works in your EPUB file, then simply leave those elements alone and let them do their job. For other elements that you’re not happy with, you can simply override them with your custom CSS. If you prefer to not write your own EPUB CSS, simply export your EPUB file without choosing any additional CSS file(s) and let InDesign do all the work."
That's interesting, thanks for passing it along! Obviously I need to start reading IDM
I personally think there still ought to be an option to tell ID not to create any CSS. That way you wouldn't have to worry about making sure to override the ID-generated elements and could be certain of clean CSS.
Basically I wish all these exciting new export features had been made entirely and explicitly optional. Then we'd just need to be able to save export settings (please Adobe!) and we'd be able to have ID do as much or as little as desired every time, on a case-by-case basis.
Again, thanks for the response.