3D/Extruded Rounded Square

Hi there,

I am trying to create a 3D rounded cornered square that looks like a keyboard button.

I have tried creating a rounded square, duplicating it, layering it under the first square and then drawing the corners to connect the two like this:

However, I'm not sure if it looks right.

Should the corners have a straight join from the top of the square and then going into a rounded part. Not sure how to explain that, but something like this:

(Obviously this is just rough and not merged with the underneath layer etc)

Can anyone recommend a way of creating such a button? I have also tried the 3D extrude option in Illustrator, but need the button to be solid colour/shapes.

Also, just out of interest, should the button have a straight edge or is the first image with the rounded corners correct?

Thanks!