Well you don't really have to worry about IE7 code not working in IE8 because IE8 has compatibility mode (it can render pages the same as IE7). But if you still want to target different versions of IE, a way that's been done for a while now is to either use conditional comments or begin your css rule with a * to target IE7 and below. Or you could pay attention to user agent on the servers and dish up a different CSS file based on that information.