The left hand column is a fake. It is partly created by a wide left hand border on postright which must be the same width as postleft and have the same background colour.
Its this part of base.css
/* 7.1 This is the basic structure. */
DIV.postleft, DIV.postfootleft {
FLOAT:left;
WIDTH: 18em;
OVERFLOW: hidden
}
DIV.postright, DIV.postfootright {
BORDER-LEFT-WIDTH: 18em;
BORDER-LEFT-STYLE: solid
}
And this part of the colour scheme stylesheet
DIV.postright, DIV.postfootright {BORDER-LEFT-COLOR: #f1f1f1}
If you want the left and right columns to have the same background colour you can just change this
DIV.postright, DIV.postfootright {
BORDER-LEFT-WIDTH: 18em;
BORDER-LEFT-STYLE: solid
}
To this
DIV.postright, DIV.postfootright {MARGIN-LEFT: 170px}