Normally a scrollbar is positioned like this:
________________________________________
| | |
| content | scro
I think thats not possible by assigning a right margin to a right-aligned scrollbar. The scrollbar is part of the window-UI and may not be styled via CSS.
However you can just create an content-wrapper around all other elements of your HTML, give it a max-width, which is smaller then 100% and set overflow: scroll;
for the wrapper. This will achieve the desired effect and work in nearly all browsers.
[personal opinion] I think it's a very bad habit of certain web-designers, who want to control every piece of my screen. For example the scrollbars should be styled by the window-manager not by the website I'm currently viewing.