if it is because it is epub3, then either try an app with a dedicated epub3 renderer option - like Bookari pro, or convert the book to epub 2 with sigil or calibre and see how moon gets on with the converted book.
a calibre epub to epub conversion on default settings will change e3 to e2. I always convert, mostly because epub2 is more tweakable. I save a copy of the original epub3, just in case, but tweak the reading copy.
another option is to use the free kobo for android reader, just for that book, as you say it looks ok in kobo.
google play store has it:
https://play.google.com/store/apps/details?
id=com.kobobooks.android
->iceyoghurt. Mon+ is a great epub reader which fully supports CSS in epub, with many many options for enabling/disabling specific CSS elements. try examining the preferences options before making silly statements