Although a dark 'border-bottom' is necessary in some occasions (to add
contrast between the page's content and the navbar itself), the other
borders were totally unnecessary.
Moreover, having a complete border causes complications to calculate the
sidebar height and to manage buttons' size and line-height.
This fix will keep the border-bottom only, removing the other ones.
Compensation rules ("- 2px") are no longer necessary.
stefanorigano
219edc67a2