The CSS syntax module describes, in general terms, the structure and syntax of cascading stylesheets, or CSS. It defines CSS as the language for describing the rendering of structured documents (such as HTML and XML), on the web and elsewhere.

This module doesn't define any properties, data types, functions, or at-rules. Rather, it elaborates on how all of these features should be defined and how user agents should parse CSS.

Reference

At-rules and descriptors

• none

NOTE

The module explicitly states that @charset is not an actual at-rule, but rather an unrecognized legacy rule that should be omitted when a stylesheet is grammar-checked. The only valid @charset usage is at the very beginning of a stylesheet, where it is interpreted as a special byte sequence stripped before processing the content.

Key concepts

• at-rule
• character escaping
• CSS comments
• CSS declaration
• CSS declaration block
• CSS function
• Invalid
• Style rule

Glossary terms

Guides

• Introduction to CSS syntax: declarations, rulesets, and statements

  • Explains the overall CSS syntax and how declarations, declaration blocks, rulesets, and statements form the style rules.

• Value definition syntax

  • Explains the formal grammar for defining valid values for CSS properties and functions, along with semantic constraints. A guide for understanding CSS component value types, combinators, and multipliers.

• CSS error handling

  • Overview of how browsers handle invalid CSS.

• Learn CSS first steps: CSS syntax

  • Introductory guide to CSS, including an introduction to CSS syntax.

Related concepts

CSS selectors module:

• CSS specificity

CSS cascading and inheritance module:

• @import at-rule
• important flag
• Initial values
• Computed values
• Used values
• Actual values
• CSS inheritance

CSS custom properties for cascading variables module:

• custom property (--*)
• var function

CSS conditional rules module:

• @media at-rule
• @supports at-rule

CSS Object Model (CSSOM) API:

• cssText property
• `CSSStyleSheet.insertRule()", "insertRule(rule)")}} method
• `CSSStyleSheet.replace()", "replace(text)")}} method

WHATWG specification:

• element
• element
• class attribute
• rel attribute

Specifications

See also

• CSS at-rule functions
• CSS selectors module
• CSS values and units module