At-rules start with an at-keyword (an '@' character followed immediately by an identifier), and consist of everything up to and including the next semicolon (;) or declaration block, whichever comes first.
At-rules
@charset
Sets the character set for an external style sheet.
@font-face
Sets a font to embed in the HTML document.
@import
Imports an external style sheet.
@media
Sets the media types for a set of rules in a styleSheet object.
@page
Sets the dimensions, orientation, and margins of a page box in a styleSheet.