RESPONSIVE AND ADAPTIVE DESIGN - Practical CSS3: Develop and Design - page 314

@ VIEWPORT

Yo u m i g ht b e t h i n k i n g t h at t h i s v i e w p o r t t h i n g s m e l l s l i like p re s e nt at i o n
rather than content so should probably be handled using some kind of
CSS construct rather than an HTML meta tag. Some clever folks at Opera
agree and have produced the @viewport rule spec ( http://dev.w3.org/csswg/
css-device-adapt/#the-viewport-rule), which defines the same functionality
as Viewport meta tag but as a CSS construct. The different options avail-
able in Viewport meta tag all have their equivalents in @viewport , except
target-densitydpi (hopefully, this will be added later):

@-o-viewport {
: ;
: ;
: ;
: ;
: ;
: ;
}

Note that @viewport currently works only in Opera Mobile 11 and later, but
in my opinion it is a better implementation than Viewport meta tag, and
should catch on in the future.