I know this is really old, but I'm posting my solution anyways since google finds this thread.
background-image: url('./imagefolder/image.jpg');
That is what I do. Two dots means drill back one directory closer to root ".." while one "." should mean start where you are at as if it were root. I was having similar issues but adding that fixed it for me. You can even leave the "." in it when uploading to your host because it should work fine so long as your directory setup is exactly the same.