CSS gradient渐变之webkit核心浏览器下的使用

http://www.zhangxinxu.com/wordpress/2010/04/css-gradient%E6%B8%90%E5%8F%98%E4%B9%8Bwebkit%E6%A0%B8%E5%BF%83%E6%B5%8F%E8%A7%88%E5%99%A8%E4%B8%8B%E7%9A%84%E4%BD%BF%E7%94%A8/