Editing the placement of columns in a 3 column fixed width theme

Here is the site I am referring to: https://russwbeck.com/test/

I can’t figure out how to get the text farther to the left. I’d like to shift it by about 250 pixels. I can make the width of that middle column (with the posts in it) larger or smaller, but it is locked in place on the left side. When I edit the size of the column, it always stretches right. I’m 99.99% sure I have to edit something in the style-sheet, but I can’t find it. I have only minimal .css experience. So any help would be greatly appreciated.

Thanks in advance!