Thank you that worked. One more question - the font is changing size when the print margin changes (shrinking when the margin is bigger). Is there a way to stop that happening?
Maybe it's simpler if I say what I'm trying to accomplish. I print out a portion of my TW to use as lecture notes, and I like to have space to annotate these notes on the right hand side. On the computer screen I want the tiddler to cover the whole screen (depending if I have the sidebar displayed or toggled off), but when printing I only want it to cover part of the page.