cant edit css file

I cant seem to edit the css file without having my files go inactive for some reason. I tried uninstalling, reinstalling, even editing the css while the plugin wasnt activated and then activated it…no luck. I am simply trying to edit the hover color, and change the width of the email and subscribe box so that they both exist on one line, the box says subscribe, and when you hover over it it changes color….Normally I would believe this to be easy css changes, but still no luck..Any help would be greatly appreciated.

http://wordpress.org/plugins/feedburner-form/