I have css like this:
background:url(data:image/gif;base64,RSDJHJV2397HJAS878324H3) top left no-repeat;
By the time DokuWiki is done processing it, it looks like this:
A path is incorrectly added, which breaks the image, and the trailing right-paren, semicolon and parameters are stripped. If you turn on css compression and go in using Firefox, all css after this line is ignored. Other browsers (IE and Chrome) recover gracefully.
That base64 in this example isn't a real image. You can create valid data by using the linux "base64" command on an image file.