What are the uses of @ in css

The @ command is often used in CSS code and has various functions. The syntax structure is basically the same. @ is followed by a keyword to specify their respective functions.

at-rule is a statement that provides instructions for CSS execution or how to behave. Each declaration begins with @, followed by an available keyword, which acts as an identifier to indicate what the CSS should do. This is a general syntax, although there are other syntax variations for each at-rule.

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General rules

General rules follow the following syntax:

The code is as follows :

@[KEYWORD] (RULE);

@charset

This rule defines the character set used by the browser if the style sheet contains non-ASCII characters (e.g: UTF-8). Note that the character set placed in the HTTP header will override the @charset rule

The code is as follows:

@charset "UTF-8";

@import

This rule indicates the requested stylesheet, here One line, if the content is correct, will bring in an external CSS file.

The code is as follows:

@import 'global.css';

Although popular CSS preprocessors support @import, it should be noted that their working principles are different from native CSS: the preprocessor will crawl CSS files and process them into a CSS file. For native CSS, each @import is a separate HTTP request.

@namespace

This rule is very useful for applying CSS to XML HTML (XHTML), because the XHTML element can be used as a selector in CSS.

The code is as follows:

/* Namespace for XHTML */
@namespace url(http://www.w3.org/1999/xhtml);
/* Namespace for SVG embedded in XHTML */
@namespace svg url(http://www.w3.org/2000/svg);

Nested rules

Nested rules contain additional subset declarations, some of which can only be used in specific situations.

The code is as follows:

@[KEYWORD] {
/* Nested Statements */
}

@document

This rule specifies conditions for the style sheet: it can only be applied to specific pages. For example, we provide a URL and then customize the styles for this specific page. In other pages, these styles will be ignored.

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The code is as follows:

@document
/* Rules for a specific page */
url(http://css-tricks.com/),
/* Rules for pages with a URL that begin with... */
url-prefix(http://css-tricks.com/snippets/),
/* Rules for any page hosted on a domain */
domain(css-tricks.com),
/* Rules for all secure pages */
regexp("https:.*")
{
/* Start styling */
body { font-family: Comic Sans; }
}

@font-face

This rule allows Loading custom fonts on web pages has varying degrees of support for custom fonts, but this rule accepts statements to create and serve these fonts.

The code is as follows:

@font-face {
font-family: 'MyWebFont';
src: url('myfont.woff2') format('woff2'),
url('myfont.woff') format('woff');
}

@keyframes

Among many CSS properties, this rule is the basis of keyframe animation and allows us to mark the beginning and end of animation.

The code is as follows:

@keyframes pulse {
0% {
background-color: #001f3f;
}
100% {
background-color: #ff4136;
}
}

@media

This rule contains conditional statements that can be used to specify styles for specific screens. These statements can include screen sizes, in screen-fit styles It will be very useful.

The code is as follows:

/* iPhone in Portrait and Landscape */
@media only screen
and (min-device-width: 320px)
and (max-device-width: 480px)
and (-webkit-min-device-pixel-ratio: 2) {
.module { width: 100%; }
}

Or only use the style when printing the document

The code is as follows:

@media print {
}

@page

This rule defines styles for individual pages that will be printed. In particular, it can set margins for page pseudo-elements: :first, :left and :right

The code is as follows:

@page :first {
margin: 1in;
}

@supports

This rule can be tested The browser knows whether a feature/functionality is supported, and if the conditions are met, specific styles will be applied to these elements. A bit like Modernizr, but really CSS properties.

The code is as follows:

/* Check one supported condition */
@supports (display: flex) {
.module { display: flex; }
}
/* Check multiple conditions */
@supports (display: flex) and (-webkit-appearance: checkbox) {
.module { display: flex; }
}

Summary

at-rule can make CSS do some crazy and interesting things. Although the examples in the article are basic, you can see how they can be used with styles for specific conditions to create user experiences and interactions that match specific scenarios.

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