Printing carried whatever theme was on screen: a dark reader printed a
dark sheet, message body included -- that renders in a shadow root, and
follows the app palette through inherited custom properties, so no rule
in this stylesheet could reach it. The print block now pins the palette
tokens themselves to a light, unpainted set, which reaches the body the
same way the theme does. Backgrounds go white rather than the light
theme's greys; a printer should not lay ink over the whole page.
Page one was also blank apart from the subject. `break-inside: avoid` on
the message card cannot be honoured by a message taller than a sheet,
and Chrome answers by moving the card to a fresh page and breaking it
there anyway. Only the header is indivisible now, kept with the body
that follows it.