CSS background image in responsive grid

I'm a Noob experimenting with Omega. My subtheme is built out of the Alpha HTML5 starterkit. As a test, I'm able to change the page background colors through the responsive sizes by placing CSS into each of the mytheme-alpha-default-sizename.css:

#page {
background-color: pink;
}

Of course, one size is pink, the next is yellow, etc. Works great.

However, I cannot do the same with a background image using this code:

#page {
background-color: pink;
background-image: url(file:///titian/Users/sb/Sites/OmegaTest/sites/all/themes/omegatestsub/images/FabricSoftGrid.png)
}

(Since it didn't show up in my preview, I'll add that the full path name ends in images/imagename.png) Again, I use a different image for each responsive size. The image is not applied in any case.
Thanks in advance for your input.