1.webkit
-webkit-gradient(radial,190,190,10,200,90,10,from(#555),to(rgba(255,255,255,0),color-stop(0.4,#123)));
应用于background-image,-webkit-border-image,content,list-style
2.moz
-moz-linear-gradient(left,black,20% rgba(...),50% rgba(...));
-moz-repeating-linear-gradient...
3.IE
filter:progid:DXImageTransform.Microsoft.Gradient(gradientType=0,startColorStr=#999FF,endColorStr=#ffffff);
.渐变可用于内容（content）填充，《html5+css3》p4039
设置渐变背景：-moz-linear-gradient(right,rgba(255,255,255,0),rgba(255,255,255,1)),url(img/bck.jpg);//background设置多个背景时，前面覆盖后面的