Does this give a clue
If I save the demo.docx as filtered HTML and convert that to EPUB I see this
If I convert the demo.docx to EPUB I see this.
I rarely use MOBI so I'm not sure what happens with it, it looks a bit messy in Mobipocket Reader - but I may have messed up the conversion from ZIP to MOBI
Added : I use Word 2007, I believe the Code style is a 2013 feature.
BR