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>>>>>>>>>>>>>>>>>>>>>>>>>>The appearance of a web page can be controlled with a CSS file. The At-Regel is an important part of this file.

What is a At-Regel?

A At-Regel is a CSS statement that can be used to control the output of a web page on a computer monitor or smartphone display and its content. At-Regel n begin with the at sign “@” followed by what is called an identifier that defines the statement. Each of these rules is terminated with a semicolon “;” or another CSS statement. The all general structure is @IDENTIFIER (RULE); – to example @Chartset “utf-8”;

Use and effect of the At-Regel

About 20 At-Regeln are available for use in a CSS file. Commonly used At-Regeln are:

  • @charset – instructs the browser to use a specific character set.
  • @import – includes an external stylesheet
  • @namespace – prefixes all content with a XML namespace

These rules are always executed. So-called conditional At-Regeln are only executed when a certain condition is met.

Example of a conditional At-Regel

Conditional, so-called group rules are defined in CSS Conditionals Level 3. An example of a conditional rule is @media. This statement is used to query the size of the display of the device on which a web page is being shown, so that the display can be controlled accordingly. Each conditional rule can contain a virtually unlimited set of nested statements.

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