Outlines are included in the CSS3 specification and allow both a border and an outline to be applied to a single element.
The outline property is identical to the border command. The additional offset property however allows the border to be moved further inside or outside of the element.
I used outlines to give borders 2 different colors, change the code to give your borders 2 different sizes.
#box {
border: 1px double #000;
outline: 2px solid #699;
outline-offset: -9px;
}