|6 Add another layer (Layers>New Raster Layer).
Load the Button selection (Selections>Load From Alpha Channel)
Contract selection by 5 (Selections>Modify>Contract)
Save this selection to alpha channel for later use (i.e. Colorize) and name it Inside Button
Apply a Linear Gradient Fill to your current selection using the settings below.
Linear Gradient Settings:
Fill Style = Linear Gradient
Blend Mode = Normal
Paper Texture and Match Mode = None
Under the Flood Fill Options Tab
Gradient = Metallic
Angle = 0
Repeats = 0