londrum - 7:44 pm on Mar 10, 2012 (gmt 0)

its probably something to do with the URL. is the image in the same directory as the html file? that would work okay for the inline method.
but if you try it with a css file, then the way you've got it written at the moment, the image would have to be in the same directory as the css file.

try changing
background-image: url("skystrip.gif");
to
background-image: url("/directory/skystrip.gif");
or wherever it is that the image is stored