How to change .discussionList .sectionHeaders background?

Hi guys!
I am trying to change selected element (in attachement to post)

I want to set new background-image to this line.
I modified discussion_list.css - added background property to ".discussionList .sectionHeaders" element.

Seems it's all right, but I have following problem:
This file
http://mysite/forum/css.php?css=discussion_list,inline_mod,moderator_bar&style=3&d=1323855242 (which automatically included in forum head section)
does not have my changes,
but if I manually open "http://mysite/forum/css.php?css=discussion_list", I see my changes.

What to do here?