@media

语法

@media 规则可置于您代码的顶层或位于其它任何@条件规则组内。

/* At the top level of your code */
@media screen and (min-width: 900px) {
  article {
    padding: 1rem 3rem;
  }
}

/* Nested within another conditional at-rule */
@supports (display: flex) {
  @media screen and (min-width: 900px) {
    article {
      display: flex;
    }
  }
}

有关媒体查询语法的讨论，请参阅使用媒体查询。

正式语法

@media <media-query-list> {
  <group-rule-body>
}
where 
<media-query-list> = <media-query>#
where 
<media-query> = <media-condition> | [ not | only ]? <media-type> [ and <media-condition-without-or> ]?
where 
<media-condition> = <media-not> | <media-and> | <media-or> | <media-in-parens>
<media-type> = <ident>
<media-condition-without-or> = <media-not> | <media-and> | <media-in-parens>
where 
<media-not> = not <media-in-parens>
<media-and> = <media-in-parens> [ and <media-in-parens> ]+
<media-or> = <media-in-parens> [ or <media-in-parens> ]+
<media-in-parens> = ( <media-condition> ) | <media-feature> | <general-enclosed>
where 
<media-feature> = ( [ <mf-plain> | <mf-boolean> | <mf-range> ] )
<general-enclosed> = [ <function-token> <any-value> ) ] | ( <ident> <any-value> )
where 
<mf-plain> = <mf-name> : <mf-value>
<mf-boolean> = <mf-name>
<mf-range> = <mf-name> [ '<' | '>' ]? '='? <mf-value> | <mf-value> [ '<' | '>' ]? '='? <mf-name> | <mf-value> '<' '='? <mf-name> '<' '='? <mf-value> | <mf-value> '>' '='? <mf-name> '>' '='? <mf-value>
where 
<mf-name> = <ident>
<mf-value> = <number> | <dimension> | <ident> | <ratio>

媒体特性

Media features describe specific characteristics of the user agent, output device, or environment. Media feature expressions test for their presence or value, and are entirely optional. Each media feature expression must be surrounded by parentheses.

示例

@media print {
  body { font-size: 10pt; }
}

@media screen {
  body { font-size: 13px; }
}

@media screen, print {
  body { line-height: 1.2; }
}

@media only screen 
  and (min-width: 320px) 
  and (max-width: 480px)
  and (resolution: 150dpi) {
    body { line-height: 1.4; }
}

媒体查询第4级引入了一种新的范围语法，在测试接受范围的任何特性时允许更简洁的媒体查询，如下面的示例所示：

@media (height > 600px) {
    body { line-height: 1.4; }
}

@media (400px <= width <= 700px) {
    body { line-height: 1.4; }
}

更多示例，请查看使用媒体查询。

可访问性

为了最好地调整网站文本大小，当您需要<length> 进行媒体查询时，请使用em。

em和px都是有效单位，但如果用户更改浏览器文本大小，em的效果会更好。

考虑使用4级媒体查询来改善用户体验。 例如，使用prefers-reduced-motion以检测用户是否已请求系统最小化其使用的动画或动作量。

规范

浏览器兼容性

更多资料

• Using media queries
• 在 JavaScript里, @media can be可以通过css对象模型接口被调用 .CSSMediaRule.
• Extended Mozilla media features
• Extended WebKit media features