/***** Selector Hacks ******/
 
/* IE6 and below */
* html #uno { color: red }
 
/* IE7 */
*:first-child+html #dos { color: red }
 
/* IE7, FF, Saf, Opera */
html>body #tres { color: red }
 
/* IE8, FF, Saf, Opera (Everything but IE 6,7) */
html>/**/body #cuatro { color: red }
 
/* Opera 9.27 and below, safari 2 */
html:first-child #cinco { color: red }
 
/* Safari 2-3 */
html[xmlns*=""] body:last-child #seis { color: red }
 
/* safari 3+, chrome 1+, opera9+, ff 3.5+ */
body:nth-of-type(1) #siete { color: red }
 
/* safari 3+, chrome 1+, opera9+, ff 3.5+ */
body:first-of-type #ocho { color: red }
 
/* saf3+, chrome1+ */
@media screen and (-webkit-min-device-pixel-ratio:0) {
#diez { color: red }
}
 
/* iPhone / mobile webkit */
@media screen and (max-device-width: 480px) {
#veintiseis { color: red }
}
 
 
/* Safari 2 — 3.1 */
html[xmlns*=""]:root #trece { color: red }
 
/* Safari 2 — 3.1, Opera 9.25 */
*|html[xmlns*=""] #catorce { color: red }
 
/* Everything but IE6-8 */
:root *> #quince { color: red }
 
/* IE7 */
*+html #dieciocho { color: red }
 
/* Firefox only. 1+ */
#veinticuatro, x:-moz-any-link { color: red }
 
/* Firefox 3.0+ */
#veinticinco, x:-moz-any-link, x:default { color: red }
  
/***** Attribute Hacks ******/
 
/* IE6 */
#once { _color: blue }
 
/* IE6, IE7 */
#doce { *color: blue; /* or #color: blue */ }
 
/* Everything but IE6 */
#diecisiete { color/**/: blue }
 
/* IE6, IE7, IE8 */
#diecinueve { color: blue\9; }
 
/* IE7, IE8 */
#veinte { color/*\**/: blue\9; }
 
/* IE6, IE7 — acts as an !important */
#veintesiete { color: blue !ie; } /* string after! can be anything */

VIA: paulirish.com