I can think of 2 ways of doing this.
My first method would be to use a pseudo selector, what this does is add content, or styles :before
or :after
an element. So in effect you can have 2 styles for one element, just one as normal, and then some extras added either before or after this element.
I have added a border-top, as normal, and then added another border-top with the pseudo selector.
My second solution is to add a box-shadow, that instead of normally looking like a diffused shadow, it styled to look like a solid shadow above the element.
I've created a jsFiddle which will hopefully give you an idea, but if you don't understand just say.
jsFiddle