The moment that you log into Cc and navigate to your planbook, our undo begins keeping a list of every action you’ve taken that affects the permanent state of your classes. If you do something you don’t like, just click the undo button at the top, right of your screen and you’ll see a description of the last action you’ve taken. Click it and Cc will undo that action. Click the button a second time and the undo button will undo the second to last action your took.
You can even undo any edits you’ve made to the text of a lesson. That said, the universal undo button will not track every single little change you’ve made to the text of a card. It will only let you undo everything you did in between putting your cursor in a text box and taking it out. If you want to undo smaller text changes, then just use the mini undo and redo buttons in the rich text bar.
Note: The undo button does not remember everything you’ve done all the way back to the beginning of time. Every time you log out or close a browser you’re resetting the actions the undo button will remember.