Data which is not backed up does not exist. This includes scripts. We have all done this at sometime or other, the important thing is to learn the lesson.
Bluehost do not do backups for you (see their knowledge base). Furthermore the Terms of Service make quite clear that it is your responsibility to take your own backups (General 11.2).
But you probably know this already, which is why you're asking the question on SO. Unfortunately, if you don't have a copy of your latest CSS file there is not much we can do for you.
Now, Bluehost will take backups for their own purposes. It is just possible that they have a backup with the version of your file that you need. So it is worth asking them nicely if they have it, and if they can send you a copy.
Otherwise you can comfort yourself with the knowledge that fixing your broken CSS won't take you as long as writing it in the first place.