I have started a new wiki - the Etsusa Bridge Wiki - and as you can see via the link there is a vertical bar running through the middle of the page (I have made the main body semi-transparent so you can see it better). Obviously this is the work of the 'middle' option that is accessed via the customize tab in Theme Designer.
Since I have (at the moment) a custom graphic that serves as the wiki's background, I am sure you can agree that the vertical bar is undesirable. However, I cannot figure out a way to remove it in any fashion. Am I missing something extraordinarily obvious, or...?
(Also: Please excuse the general look of the homepage/wiki. It is new, and my experience with CSS/HTML is not broad).
I should advise that I am currently on an archaeological dig, and I can only access wifi in the village square. I hope you will understand if I cannot respond promptly.