@-rule

CSS @-rules, or at-rules, are instructions or directives to the CSS parser. They can be used for a variety of purposes.

The  at-rule can be used to specify the character encoding of an external style sheet. It must appear before anything else in the file.

The  at-rule allows users to import one style sheet into another. All  at-rules must appear before any rules.

The  at-rule lets users target rules to the media types they specify.

The  at-rule can be used to specify margins for paged media. You can set different margins for left- and right-hand pages when you’re printing double-sided pages, as well as for the first page.

The  at-rule allows users to specify custom fonts.

The  at-rule in CSS3 lets users declare an XML namespace, as well as an optional prefix with which that namespace can be specified.