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At-rules

At-rules are CSS statements that instruct CSS how to behave. They begin with an at-sign, @ (U+0040 COMMERCIAL AT), followed by an identifier. They include everything from the at-keyword up to the next semicolon, ; (U+003B SEMICOLON), or the next CSS block, whichever comes first.

At-rules are used to group and structure style rules and other at-rules, declare style information not directly associated with selected content, and manage syntactic constructs such as imports and namespaces keyword mappings.

Syntax

The at-rule is defined in the CSS syntax module, with different at-rules being defined in their respective modules. They generally take one of two forms depending on the specific rule and its purpose: statement at-rules and block at-rules, which can contain nested qualified rules, at-rules, or declarations.

Statement at-rules

/* General structure */
@identifier (RULE);

/* Example: tells browser to use UTF-8 character set */
@charset "utf-8";

Statement at-rules end in a semicolon. There are several statement at-rules, designated by their identifiers, each with a different syntax:

@charset: An algorithm (has the syntactic form of an at-rule, but isn't a definition) that determines the fallback character set used by the style sheet (CSS Syntax).
@import: Tells the CSS engine to include an external style sheet (CSS cascading and inheritance).
@layer: Defines the order of precedence in case of multiple cascade layers (CSS cascading and inheritance). Also used as a block at-rule to define a layer's styles.
@namespace: Defines a default namespace for a style sheet or a namespace prefix that a selector only matches if the namespace and other selector components match (CSS namespaces).

Block at-rules

@identifier (RULE) {
}

Block at-rules end in a {}-block that contain nested rules, other at-rules, or property or descriptor declarations.

@counter-style: Define custom counter styles and extend predefined list styles (CSS counter styles).
@container: A conditional group rule that applies its content if the container meets the <container-condition>s (CSS containment).
@font-face: Defines font resource locations, both local and external, along with the style characteristics for when those resources are used with a declared font-family (CSS fonts).
@font-feature-values (plus @swash, @ornaments, @annotation, @stylistic, @styleset and @character-variant): Controls font display per font-family by defining font-specific alternates, or custom names, to feature indexes in font-variant-alternates in OpenType (CSS fonts).
@keyframes (and the @-webkit-keyframes alias): Define a named animation by describing defining CSS styles for intermediate steps (or keyframes) in the animation sequence (CSS animations).
@layer: Creates a named cascade layer with the CSS rules for that layer inside (CSS cascading and inheritance). Also used as a statement at-rule to define the order of precedence in case of multiple cascade layers
@media: A conditional group rule that applies its content if the device meets the criteria of the condition defined using a media query (CSS conditional rules).
@page: Specifies aspects of a page to be printed, such as its dimensions, orientation, and margins (CSS paged media).
@position-try: Defines custom position options which can be used to define fallback positioning and alignment options for anchor-positioned elements (CSS anchor positioning).
@property: Defines a CSS custom property, allowing for property type checking and constraining, setting default values, and defining whether a custom property can inherit values or not (CSS custom properties for cascading variables).
@scope: Defines a scope in which to apply them to selected elements and the styles to apply to the elements in that scope (CSS cascading and inheritance).
@starting-style: Define the starting property values for an element to transition from when the element receives its first style update, such as when transitioning from display: none (CSS transitions).
@supports: A conditional group rule applies its content if the browser supports the CSS features of the given condition (CSS conditional rules).
@view-transition: Opts the current document into a view transition, and the destination document as well in the case of cross-document navigation transitions.

Index

Specifications

Specification
CSS Syntax Module Level 3>