Doesn't just this work?:
Code:
@page { margin: 5pt; }
html body { margin: 0; padding: 0; }
(Note there's no comma between "html" and "body", meaning "body inside html" instead of "body and html". I use this because in my Cybook, "body" alone seems to be overriden by some internal style of the reader, while "html body" has a higher priority and gets the effect done.)