纯css页面变灰度兼容ie、firefox、chrome、opera、safari

html {
-webkit-filter: grayscale(100%);
-moz-filter: grayscale(100%);
-ms-filter: grayscale(100%);
-o-filter: grayscale(100%);
filter:progid:DXImageTransform.Microsoft.BasicImage(grayscale=1);
_filter:none;
}