Can't remove borders from main content area

Hello,

New to this theme and just trying to customize it a little from a small personal project.

I generated a theme from Adaptive themes and am trying to remove the left/right/bottom border between the main content area and the body; there seems to be nowhere in the appearance settings; I can change colours and other options, but I want to remove the border around the main content area entirely (attached screenshot).

Is there a setting I'm missing somewhere? I've tried adding custom CSS of

{
border: 0px solid white;}

to any element that might be causing that, but nothing will make it go away. Is there a reason for not having a setting for removing those borders?

Thanks!