CSS Browser Detection

.myclass {
  color: red;     /* All browsers [Target: FF,NS] */
  _color: green;  /* IE6- [Target: IE6-] */
  .color: blue;   /* IE7, IE6- [Target: IE7] */
}
body:last-child:not(:root:root) .myclass {
  color: purple;  /* Safari, Konqueror [Target: Safari, Konqueror] */
}

For IE8 You can just use meta tag to make it behave like IE7 (Facebook, Google are using this technique)

<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7" />