PHPBB3 Change width?

I want to make my forums 960px instead of 100%, anyone know how to do this?

I tried changing the wrap style in common.css but this didn't work.

 

ACP -> Styles -> Theme -> EDIT

Find the section labeled


/* Main blocks
---------------------------------------- */

and then change/add under that:

width:960px;

 

Which one are u using subsilver or prosilver

 

I'm using prosilver.

I did the instructions above but you didn't mention that I have to edit the wrap style. Note I also removed the min-width parameter and set the margin left and right to auto in order to center it.

#wrap {
padding: 0 20px;
width:960px;
margin-left:auto;
margin-right:auto;
}