All selectors provided here are valid for CSS 2.1 unless otherwise stated.

Internet Explorer 6, Internet Explorer 7 (Non standard mode), Internet Explorer 8 (Non standard mode):

* html {}

Internet Explorer 7, Internet Explorer 8 (IE7 standard mode):

*:first-child+html {}
 * + html/*/ * /**/ body {}

Internet Explorer 8 (Ids are examples):

#ie_80 {} /* IE8 */
 #ie_80, #ie8#fix {} /* other browsers */

It’s not Internet Explorer 6:

html>body {}

It’s not Internet Explorer 6, It’s not Internet Explorer 7:

html>/**/body {}

It’s not Internet Explorer (only valid for CSS3):

:root {}

Safari 3, other Webkit browsers (only valid for CSS3):

body:not(:root:root)

It’s not Internet Explorer, It’s not Opera 9.2x or earlier:

head~body {}

It’s not Internet Explorer, It’s not Opera 9.2x or earlier (only valid for CSS3):

body:only-of-type {}

Opera between 7.2x-9.2x:

html:first-child {}