I am on one of the themes, not sure which one I am on, because I can't figure out how to change it, but it's the one with a red monster with blue sky around him, whichever one that is. Anyways, I think the buttons where you select, "General" "RuneScape" "Gaming" etc need to be changed to fit the theme better. They don't belong as they are. Just my opinion though.
The blue doesn't go with the theme. Tbh, the background is out of place. I hate just the white/black it feels too plain. Maybe try lighter colors, but not black/white? Tip.it is a good example of light but color variation (though I'm not suggesting to use their theme or any form of it). Just wanted to give an example.