set the wiidth of the gkContentMainbody container

Hi there
is it possible to set the width of the ContentMainbody. In the template settings i use Template Width: Auto but it would be great to display the content smaller. Where do I have to correct these settings.

I have tried in template.css the line
#gkContentMainbody { width: auto; background:transparent; overflow:hidden; }

If i change the settings width it does not makes any changes.

Attached you'll find the screenshot with loaded content.
Sincerely
Andreas

Well template mainbody needs to be 100 percent so it can fill empty space depending on which column layout you are using as well as any other modules...

If you can be more specific on what you want e.g taking a screenshot and edit on it on how you want it to look so we can see and understand better...