Take a brush now of black color with blurred edges and paint the lowest part of the marked region.

Merge down now all the layers composing the button in a group. Copy this new made group and place it the same way it is demonstrated below. On the copy must be changed the parameters, insert those indicated below.

The second layer:
Blending Options-Gradient Overlay

Gradient’s parameters:

Blending Options-Stroke

Gradient’s parameters: