I'm also having problems with Moon+ with CSS formatting. However, I was also able to replicate the problem that you described.
I found a solution. I'm assuming you're using an android device.
This is what I get when I press on the ePub link and chose to open directly with Moon+.
What I usually do is open it with a browser app first.
And then pull down the notification tray and then choose Moon+ to open the file. And voila.
