css help

Hello: I hope this is easy for someone to answer; I am trying to put sidebar on “posts” in 2011 theme. I am using a child theme. I got the “get sidebar” thing added to the “single.php” file and it is now showing on the post pages. The problem is that the sidebar is not displaying properly; it makes it so the post content drops below the sidebar; the post content is “centered” on the page which is part of; if not all of the problem…

i found this css which is causing it to be centered:
.singular {margin: 0 auto;}

now using firebug when i remove the “auto” from that css statement it pushes the post content over to left which looks like it may fix the whole problem; if it doesnt I know it will at least help…

but I do not know how to “undo” that css statement (from core wordpress) in my child themes css file; what would I do to “undo” the “auto” or the whole thing?

Can anyone help?

Thanks, Gerard