How do I use the --user-style-path parameter with CutyCapt to apply a CSS style?  I'm using a command similar to this:
$ xvfb-run --server-args="-screen 0, 1280x720x24"  \
    CutyCapt --url=http://cutycapt.sourceforge.net \
    --out=/home/pi/image.png \
    --user-style-path=/home/pi/dark.css
dark.css contains body { background-color: #888; }
Currently I'm able to get an image, but it does not apply the style.  If I give it a path that doesn't exist, I don't seem to get any errors so I think I'm missing something here.
I've tried prefixing the path with file:// and
I've also tried using --user-style-string wrapped with single or double quotes to no effect.
This code is running on a headless Pi using Linux.