Prestashop puts border inside div

Question

Im trying to insert this on my topmenu in Prestashop:

border-bottom: 3px solid rgba(0, 0, 0, 0.6);
background:#fff;

it makes the background white, but the border is inside ( on the white background )

when its on a normal page, its outside the box, whats going on?

Answer 1

Plz check the "box model": border-box / content-box

width + padding + border = actual visible/rendered width of box

height + padding + border = actual visible/rendered height of box

http://css-tricks.com/examples/BoxSizing/

http://www.w3schools.com/cssref/css3_pr_box-sizing.asp