For the life of me I can't remember any titles other than Divergent and Hunger Games with amped up violence in the non-magical variety but I know there is more. i'm going to have to have a look on my book shelf when I get home. OH, there's Anna Dressed in Blood, that's a good one. And to be fair, I avoid books with sex or much sexual content like the plague so I couldn't speak much on that.
Maybe someone else has some better suggestions, but there is a lot you can get away with in YA in all genres.
Actually, now that I think about it, my WIP is probably a lot
less 'dark' than the aforementioned stuff. Violent/dark things might happen, but the focus might be on something else, similar to how Marvel movie franchises et. al have Thor beating the shit out of bad guys, but very little actual blood is seen (to keep rating PG or PG-13). You could describe one event in two very different ways, IMO, it's all about execution.
Now that I think about it, my writing is pretty much pure YA, with the exception of the ages (but I've decided not to worry about that for now and just get on with it).