As for your border height issue, there is no single CSS property that will let you set a border that is 50% high.
You can set different heights for the anchor tags and list items and only apply the border to the anchor tags but this will leave you with a reduced ‘clickable’ area.
I seem to recall someone coming up with something previously in the forums that **might** be the answer but I think it involved playing around with margins?
I think it was @chrisburton but whether code still exists or not is another matter.
Perhaps a search of the site?