The problem is that you used the images from the gallery that are 100% transparent and therefore, cannot be pressed. I know this because you say that the button is only pressable on the non-tranparent part, the text.

You need to be using partially transparent(but not visible) images. To do this you will need to create a white (or other color) rectangular image is an image editor and set the transparency of the layer to either 99% or the opacity to 1%. This will give you an almost transparent button that is pressable across the entire rectangular area.

This topic has been discussed in the NG forum numerous times so you may also want to search there as well.