add padding-right to the whole t3 container

hi, i want to add a module fixed on right (like facebook) it's ok so long.
But since the desktop size container has width: 1196px;
i set for my fixed module
@media (max-width: 1550px){.fixedmodule{display:none}}

obiouvsly that size is too much, nobody noticed that module but the users with fullhd resolution.
So i want to use the facebook solution: a padding-right (or margin) to the "whole site".
In this way, like facebook, the whole site container it isn't exactly centered but a little on the left..
But i need some t3 expert for doing that safely, it's not so easy as it looks...

The attachment explains the problem, the first screen is what i have, the second what i would to have