At-rules start with an at-keyword, an "@" character, and followed immediately by an identifier (for example, @import, @page). An at-rule consists of everything up to and including the next semicolon (;) or the next block, whichever comes first.
See these Web pages for further reference:
The following table defines which CSS AT-rules are supported by Opera.
Need help? Hit F1 anytime while using Opera to access our online help files, or go here.