#grad {
  background: -webkit-linear-gradient(left top, red , blue); /* Safari 5.1 - 6.0 */
  background: -o-linear-gradient(bottom right, red, blue); /* Opera 11.1 - 12.0 */
  background: -moz-linear-gradient(bottom right, red, blue); /* Firefox 3.6 - 15 */
  background: linear-gradient(to bottom right, red , blue); /* 標準的語法 */
}


http://www.runoob.com/css3/css3-gradients.html