css3渐变透明遮盖

    background: -webkit-gradient(linear, 0 0, 0 100%, from(rgba(255, 255, 255, 0)), to(#fff));
    background: -moz-linear-gradient(top, rgba(255, 255, 255, 0), #fff);
    background: -o-linear-gradient(top, rgba(255, 255, 255, 0), #fff);
    background: linear-gradient(top, rgba(255, 255, 255, 0), #fff);
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#00ffffff, endColorstr=#ffffff, GradientType=0);
    bottom: 0;