全屏灰色

<style>
.filter {
  -webkit-filter: grayscale(100%); /* webkit */
  -moz-filter: grayscale(100%); /*firefox*/
  -ms-filter: grayscale(100%); /*ie9*/
  -o-filter: grayscale(100%); /*opera*/
  filter: grayscale(100%);
  filter: progid:DXImageTransform.Microsoft.BasicImage(grayscale=1); /*ie*/
  filter: gray; /*ie9- */
}
</style>