My 2 go-to Android epub apps, which are good with CSS, are Bookari (formerly known as Mantano) and Pocketbook (by Obreey Products).
Bookari has 2 different renderers available if you want to use an EPUB3 renderer for EPUB3s. As you said you've already tried this one I'm wondering what CSS didn't work for you? It's pretty easy to use but some of the bells & whistles are only in the premium version.
Pocketbook is not quite as easy to use because some of its features are not as easily discoverable (e.g. custom tap zones). However, all its premium features are included in the free version, so it's hard to complain about that.
It also has 2 different renderers available - one is Adobe-based the other Webkit-based - so you get 2 chances to see whether a particular book's CSS displays as you expect.