In the latest version (3.7.5), if you go to the Review icon located on the lefthand side, then select “MarginNote 3 Card Deck Sample”, there’s a misspelling in one of the words in the toolbar above. “Cloze” should be “Close”.
If you look up the word “Cloze” you will see that it is a term used to describe the hiding of words so that they can be used for recall. Clicking that with the sample open makes it clear 
ah! Thanks for the clarification I do not know that term.