1. Borders on
::before
and
::after
This is the classic approach with three transparent and one colored border. It has the disadvantage that the clickable zone of a link is still a rectangle. Go for instance to the top left corner of the second link. You will notice that you are actually already on the third link.
2. Skewing and rotating
::after
With this approach the clickable zone is identical to the visual representation of a link - you move outside of the triangle and are on the next link.
3. Cutting off with
clip-path: polygon()
A third way to achieve this is to use
clip-path: polygon()
. Browser support meanwhile is
OK-ish
.