Ok. I found a solution finally... after a month of slogging through support forums, the codex and massive trial and error.
I'm using a mac and have been doing my editing with dreamweaver and my uploading/downloading with fetch. (of course in the process, I've also used transmit, fugu, and cyberduck, which all had the same results.)
After conducting an exhaustive experiment where I opened a stylesheet in a working theme in mac's textedit, made one change, saved it and re-uploaded it, then did the same thing with dreamweaver, I determined that dreamweaver is doing what was described in Jpigford's trouble ticket, as adding the ^M mac line endings to every line. I was only able to see this after using terminal to view the style.css files using pico.
To view your file, put it where you can get at it (like the desktop) or drill down in terminal till you get to it. (I won't explain that here, sorry) and type
This will let you view your stylesheet in the pico editor which shows whether or not the proper line endings are there.
If your stylesheet code is all crammed together with lots of ^M's in there, then you have the problem I did. The next matter was to convert the file before re-uploading it to my webserver.
This page: https://www.kb.indiana.edu/data/agiz.html
gave several options for solutions.
But JUST uploading the already broken files with Fetch or any other FTP client alone did not work as they suggested. (I had already tried that with my previous experiment.) I needed to translate the file in Terminal on my mac.
I finally did it by going to the directory where the stylesheet exists and typing this in:
tr '\r' '\n' < style.css > unixstyle.css
Just for kickes, I viewed the new unixstyle.css file in pico
and it looked perfect!
Then, because I am not that skilled with navigating around unix, I went back to the file on the desktop, renamed it style.css (while disposing of the old bad file).
I then uploaded as a text file using Fetch.
Voila! It worked.
No amount of messing with tiny code typos fixed the problem. It's true what some have said, that Dreamweaver breaks the page, but no one had explained exactly how or why. For me at this point, downloading and possibly paying for a new software package isn't an adequate solution. For now, transferring this file before I upload it is a reasonable workaround. I did try to figure out how to adjust the preferences in Dreamweaver to ensure that it saves with the proper line endings, but didn't find anything that seemed to have any effect.
I hope this helps any of you who have had this same problem.