BuddyPress.org

Off the top of my head locate the min / max widths and replace them with width:960px or larger if you really wish. Child theme approach is best as then you can move a copy of the bp default css to your own folder to work on , problem is that min/max properties are a nuisance as they can’t be unset as such, once stated you are stuck with the damned things ‘auto’ is not a value for min/max nor is re-setting them to ‘0’ so the original property decs need to be removed really.