one way: in an HTML document to import under the condition of use, such as insert the following code in the HEAD:
code is as follows:

<! -- [if Internet explorer 6] >
<Link rel="stylesheet" href="" type="text/CSS"/>
<! [endif] -- >
<! - [if] IE >
<The link type="text/CSS" media="screen" rel="stylesheet" href="" title="Cleanity/>"
<! [endif] -- >

2: the conditions of use imported at the beginning of the CSS document, shown in the code below:
code is as follows:

[if SafMob] @import (' iphone CSS ');

[if! SafMob] @import (' non - iphone. CSS ');

your browser load the CSS order:
1. Load the url specified in the HTML page.
2. Parse the HTML
3. Remote access to the link tag refer to CSS file
4. Load the execution for CSS file, meet @import url (xx. " css") Such code, can remote access to xx. CSS
5. Load perform xx. CSS
by @import up to 31 CSS file can be imported, because every time a remote access to the CSS file will generate the HTTP links, more time consuming, so, had better use @import less as far as possible. 31, estimates that there are no projects will use so much.# 0 - #

This concludes the body part