Best CSS hack Application Method

For IE6

Background-color: blue;
_Background-color: red;

If both IE7 and IE6 have problems
Select either of the following two:

Background-color: blue;
*Background-color: red;

Background-color: blue;
+Background-color: red;

If only IE7

Background-color: blue;
*Background-color: red;
_Background-color: Blue;/* restore IE6 */

For IE8

Background-color: blue;
Background-color: red\ 9;/* Used for IE6, IE7, IE8, and ie9 */
*Background-color: Blue;/* restore IE6, 7 */
Background-color: Blue\ 9 \ 0;/* Restore ie9 */

For ie9 

Background-color: blue;
Background-color: red\ 9 \ 0;/* Act on ie9 */
_Background-color: Blue;/* IE6 cannot be identified, so you need to restore IE6 ~ */

For the entire IE

Background-color: blue;
Background-color: red\ 9;

! Important

Used in all browsers-it cannot be regarded as hack! Important can ignore the CSS priority.