线性渐变的兼容写法如下：

.gradient{
    background: #000000;
    background: -moz-linear-gradient(top,  #000000 0%, #ffffff 100%);
    background: -webkit-linear-gradient(top,  #000000 0%,#ffffff 100%);
    background: -o-linear-gradient(top,  #000000 0%,#ffffff 100%);
    background: -ms-linear-gradient(top,  #000000 0%,#ffffff 100%);
    background: linear-gradient(to bottom,  #000000 0%,#ffffff 100%);
    filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#000000', endColorstr='#ffffff',GradientType=0 );
}
:root .gradient{filter:none;}