Background Image In Sidebar CSS problem

Hi all,
I am attempting to add a little separation from the center content in my left and right sidebars. It is easy to just add a background color, but the color abruptly ends at whatever height I set, and I don’t like that look. Consequently, I thought I would create a vertical gradient from light gray to white. This way the background would just blend into the white page background. I created the image as a narrow .jpeg. I added

background-image: url (images/sidebar_gradient.jpg);
background-repeat: repeat-x;

to #secondary in my style sheet. Why does the background-color work, but not background-image.

Also, I have found that occasionally some CSS will not work from the style sheet, but does work if I embed it in the HTML tag. Has anyone experieinced this? Found a solution?
Thanks for any help.