CSS3 グラデーション

background: -moz-linear-gradient(left top, #990,
#c36 30%,
#f60 50%,
#000 70%,
#066);　/* Firefox用 */
background: -webkit-gradient(linear, left top, right bottom, from(#990),
color-stop(0.3, #c36),
color-stop(0.5, #f60),
color-stop(0.7, #000),
to(#066));　/* Safari,Google Chrome用 */


参照
http://www.css-lecture.com/log/css3/css3-gradient.html