IE6以下

#help_me { _color: blue; }
* html #help_me  { color: red; }

IE7

*:first-child+html #help_me { color: red; } 
*+html #help_me {  color: red; }

IE6, IE7

#help_me { /color: blue; }

IE8

#help_me { color: blue9; }

IE7, IE8

#help_me { color/***/: blue9; }

IE6以外

#help_me { color/**/: blue; }

IE6, IE7以外

html>/**/body #help_me { color: red; }

IE6〜IE8以外

:root *> #help_me { color: red;  }

モダンブラウザ Firefox

#help_me,  x:-moz-any-link  { color: red; }

Firefox 3.0以上

#help_me,  x:-moz-any-link, x:default  { color: red; }

Safari 2-3

html[xmlns*=""] body:last-child #help_me { color: red; }

Safari 2 – 3.1

html[xmlns*=""]:root #help_me  { color: red; }

Safari 2 – 3.1, Opera 9.25

*|html[xmlns*=""] #help_me { color: red;  }

Safari 3以上, Chrome

@media screen and (-webkit-min-device-pixel-ratio:0) {
#help_me  { color: red;  }
}

Safari 3以上, Chrome, Opera 9以上, Firefox 3.5以上

body:nth-of-type(1) #help_me { color: red; }
body:first-of-type #help_me {  color: red; }

Opera 9.25以上

;;body #help_me {  color: red; }
html:66irst-child #help_me {  color: red; }

Opera 8, 9以外

body[class|="hypen-ated"] #help_me {  color: red; }

iPhoneのみCSSを変える場合はiPhone用CSSを作成して読み込ませます。

<link media="only screen and (max-device-width: 480px)" href="iphone.css" type="text/css" rel="stylesheet" />

/* iPhone / mobile webkit */
@media screen and (max-device-width: 480px) {
#help_me { color: red;  }
}