hey, I had also the same issue and I did not noticed that!!!!
But it was solved. Please check to which style.css file are you assigning the permission. This should be one in your current theme directory. If you have three themes installed, you will have three .css files for each there. I assigned the permission and it solved my issue.
Also, if it does not work, you can edit the file using any other client, for example FP or FTP. ??