# http://wiki.nginx.org/HttpSubModule
http {
    sub_filter '</head>' '<style>html { -webkit-filter: grayscale(100%); /* Chrome 19+, Safari 6+, iOS Safari 6+ */
filter: gray; /* IE6-9 */
filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/></filter></svg>#grayscale"); /* Firefox 10+, Firefox on Android */ }
</style></head>';
}