Here\'s my source image:
And my source image zoomed in:
You can probably just get away with setting the border to a light colour and outline to a darker colour, then just set the border-radius. Note I haven't tested this, and if memory serves the outline does not curve with border-radius. Also note that border-radius requires several attributes to be set to become cross-browser compatible. Refer to http://perishablepress.com/press/2008/11/24/perfect-rounded-corners-with-css/ for more info.
If this fails, you could always use an inner-div, which you set to position absolute, left 0, right 0, top 0 and bottom 0 and then use that as either the inner or outer border. Setting the border-radius will definitely work then.
Regards, Richard