You can use background-gradients for that effect. For your example just add the following lines (it is just so much code because you have to use vendor-prefixes):
background-image:
-moz-linear-gradient(top, #000 10px, transparent 10px),
-moz-linear-gradient(bottom, #000 10px, transparent 10px),
-moz-linear-gradient(left, #000 10px, transparent 10px),
-moz-linear-gradient(right, #000 10px, transparent 10px);
background-image:
-o-linear-gradient(top, #000 10px, transparent 10px),
-o-linear-gradient(bottom, #000 10px, transparent 10px),
-o-linear-gradient(left, #000 10px, transparent 10px),
-o-linear-gradient(right, #000 10px, transparent 10px);
background-image:
-webkit-linear-gradient(top, #000 10px, transparent 10px),
-webkit-linear-gradient(bottom, #000 10px, transparent 10px),
-webkit-linear-gradient(left, #000 10px, transparent 10px),
-webkit-linear-gradient(right, #000 10px, transparent 10px);
background-image:
linear-gradient(top, #000 10px, transparent 10px),
linear-gradient(bottom, #000 10px, transparent 10px),
linear-gradient(left, #000 10px, transparent 10px),
linear-gradient(right, #000 10px, transparent 10px);
No need for unecessary markup.
If you just want to have a double border you could use outline and border instead of border and padding.
While you could also use pseudo-elements to achieve the desired effect, I would advise against it. Pseudo-elements are a very mighty tool CSS provides, if you "waste" them on stuff like this, you are probably gonna miss them somewhere else.
I only use pseudo-elements if there is no other way. Not because they are bad, quite the opposite, because I don't want to waste my Joker.