That is because it is no longer there. With so much css involved in various template colours etc it would have been silly to combine them in one place for the editor. It would just cause far too much confusion.
It is far easier and always was to edit them in a text editor. Yes I know that means you have to daonload them, edit them and then upload the changes each time but many work on localhost anyway. I am in the fortunate position that I can use winscp to connect to my server so I can edit live. You can also use Firebug to test your changes live before you upload them. There are many methods and you have to choose whaich is best for you and in what situation.
Me? If I need to make quick edits I just do it directly using winscp on my live server.
If I am developing a new site I always do it on my local machine using wamp and notepad++ ad my editor.