Next steps are the typical Web 2.0 shadows. I took slightly lighter foreground color (e.g. 3d8afd).
There is a special shadow tool: Filters -> Light and Shadow -> Drop Shadow . The default
values are fine for this. I disabled all other layers and only enabled the layer with the button on it(the
eye symbol in the Layer Dialog) and the used the shadow tool. This tool creates a new shadow layer.
And it look now like this