You don't really have a lot of control over the border of the rollover hit area. You can configure it to be just a thin line by leaving Show Border on but deselecting Show Runtime Border. Or you can deselect both options and show no border whatsoever for the hit area. You can change the colour of the border, but apart from these two settings, you cannot configure its width very well.
The stroke of the border on the area revealed at rollover is much more configurable.