渐变色兼容

[ckrad]

    background-image: -owg-linear-gradient(top, transparent, rgba(0, 0, 0, 0.5));
    background-image: -webkit-linear-gradient(top, transparent, rgba(0, 0, 0, 0.5));
    background-image: -moz-linear-gradient(top, transparent, rgba(0, 0, 0, 0.5));
    background-image: -o-linear-gradient(top, transparent, rgba(0, 0, 0, 0.5));
    background-image: linear-gradient(top, transparent, rgba(0, 0, 0, 0.5));

ispriter会只保留一个background-image