What happened to the dark grey background in apple books?

Recently got a new ipad. I use a Samsung phone. Don't hate me. But I LOVE the apple book app and was looking forward to having the dark grey background. Surprise, it's gone and now only black option is close. I'm so disappointed. Why? WHY! Maybe I'm just getting old. Is there a way to get it back? Guess I'll go back to using a kindle