This is a CSS trick, not a formal solution. I leave the code with the period black because it helps me position the element. Afterward, color your content (color:white) and (margin-top:-5px or so) to make it as though the period is not there.
Borders are defined per side only, not in fractions of a side. So, no, you can’t do that.
Also, a new element wouldn’t be a border either, it would only mimic the behaviour you want – but it would still be an element.