Theme CSS Q

Ok, here is another noob q. I use Arclite 1.5 from digitalnature.ro

There is a section to put specific css code in to modify theme behavior. I tried the following, in order to get all chars to be 14px:

p
{
font-size: 14px
}

it does not work. that is already above my knowledge of css. Any ideas how to fix that?