This At-Rule defines a Page Box - a special rectangular area where content
is rendered in paged media. The page area consists of the element content
and the page margin area that surrounds the content. Within an @Page At-Rule,
properties of the page box are set (margins, page layout orientation and dimensions.)
The optional Page Label and accompanying Pseudo-class determine which pages
the subsequent style declarations will apply to. The allowed Pseudo-classes
only apply in this @Page At-Rule context - :first (the first page), :left
(all left pages) and :right (all right pages.)