CSS Challenge #3

No diagram for this.

The challenge is to define some CSS so that you can do basic math operations. I have a nice working example hidden away.

The specs are

class="number operator number"

where number is one of [one, two, three, four, five, six, seven, eight, nine]

and operator is either [plus, minus]

So that if you do
<div class='three plus eight' />

you'll see say, 11 squares or some other kind of unit.

Extra points if you can make negatives work too.

You ought to be able to do it in 12 definitions or less...

good luck!