IE6:
_selector{property:value;}
selector{property:value;property:value !important;} //IE6 不支持同一选择符中的 !important
IE7:
+selector{property:value;}
IE8:
selector{property:value ;}
IE6 & IE7:
*selector{property:value;}
IE6 & IE7 & IE8:
selector{property:value9;}