OK, thanks.
I gave up on the HTML/CSS rotation because the positioning is just barmily random and I could not the page to format anything like I wanted. I read that DOMPDF does column sizing first and then does the transformation, so things don’t smush up properly across the page like I would want them to.
I’ll have another look and see if I can make the HTL/CSS rotation work, otherwise I shall give up and just moan forever about how terrible HTML/CSS layout design is!
(Postscript: even Microsoft doesn’t bother with the HTML/CSS text rotations if you export a piece of rotated text from Word or Excel – always comes out unrotated)