how to reduse dark showdow

that is an embossed shadow so yes basically its the model has an extra edge or perhaps you have two models on top of each other at rendor time

We'll need to look at how your buttons are built, because apparently there are done differently than the other ones, You can even see that the light/shadow direction isn't the same. Meaning I don't think it's a shadow, it's just how the faces are coloured. (also the corner roundness is different, it looks almost like they're images pasted on top if you get what I mean)
We need more info on this. Can you share at least a screenshot of the whole window with one of the 4 objects selected?