今天在学习jquery mobile的时候，发现css中有媒体查询这个概念，用他能够进行针对媒体设备设定不同的布局状态；

在单一文件下，css定义方式如下：

@media (min-width: 1001px) {
  #sidebar ul li a:after {
    content: " (" attr(data-email) ")";
    font-size: 11px;
    font-style: italic;
    color: #666;
  }
}

@media (max-width: 1000px) and (min-width: 700px) {
  #sidebar ul li a:before {
    content: "Email: ";
    font-style: italic;
    color: #666;
  }
}

@media (max-width: 699px) and (min-width: 520px), (min-width: 1151px) {
  #sidebar ul li a {
    padding-left: 21px;
    background: url(../images/email.png) left center no-repeat;
  }
}

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@media属性值在不同的宽度值时采取不同的样式。

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如果在想在不同的设备下引入不同的css，可以做如下定义：

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<link rel="stylesheet" href="smartphone.css" 
media="only screen and (min-device-width : 320px) 
and (max-device-width : 480px)">

<link rel="stylesheet" href="smartphone-landscape.css" 
media="only screen and (min-width : 321px)">

<link rel="stylesheet" href="smartphone-portrait.css" 
media="only screen and (max-width : 320px)">

<link rel="stylesheet" href="ipad.css" 
media="only screen 
and (min-device-width : 768px) 
and (max-device-width : 1024px)">

<link rel="stylesheet" href="ipad-landscape.css" 
media="only screen 
and (min-device-width : 768px) 
and (max-device-width : 1024px) 
and (orientation : landscape)">

<link rel="stylesheet" href="ipad-portrait.css" 
media="only screen 
and (min-device-width : 768px) 
and (max-device-width : 1024px) 
and (orientation : portrait)">

<link rel="stylesheet" href="widescreen.css" 
media="only screen and (min-width : 1824px)">

<link rel="stylesheet" href="iphone4.css" 
media="only screen 
and (-webkit-min-device-pixel-ratio : 1.5), 
only screen and (min-device-pixel-ratio : 1.5)">

实例可以参考：http://css-tricks.com/examples/MediaQueriesSidebar/

http://stuffandnonsense.co.uk/blog/about/hardboiled_css3_media_queries