-moz-linear-gradient(起始点, 其实颜色, [中间颜色 百分比], 结束颜色)。
起始点 ：left top center bottom，可以组合。
颜色 ： ragba，如果是transparent则为透明。
-moz-linear-gradient(center top, transparent, transparent 49%, rgba(2,37,58,0.5) 50%, rgba(63,111,135,0.5)); 中上开始。
opera浏览器 ：
-o-linear-gradient(top, transparent, transparent 49%, rgba(2,37,58,0.5) 50%, rgba(63,111,135,0.5));
chrome浏览器 ：
-webkit-gradient(linear, center top, center bottom, from(transparent), color-stop(49%,transparent), color-stop(50%, rgba(2,37,58,0.5)), to(rgba(63,111,135,0.5)));
百分比的写法 ：起点y 终点x
-webkit-gradient(linear, 0% 100%, 100% 100%, from(#517384), color-stop(50%, #79a3b8), to(#517384));
-moz-linear-gradient(center left, rgba(81,115,132,0.55), rgba(121,163,184,0.55) 50%, rgba(81,115,132,0.55));
