My "edit css" option on dashboard isn't showing up

I am using the child twenty-ten theme and i can’t find an option for “edit css” on my dashboard but I remember that it used to have one, because I’ve edited it before. Anyways, now that I can’t find the “edit css” option under the “appearance” tab, the changes I made on it (back when I could find the edit css option)reverted back to the original. I can still see an “editor” option but no “edit css” option. What’s going on? here is the link to my problem. as you can see, there is no edit css option because it disappeared for some reason.