What were Callie and Arizona celebrating when Callie was at home and had fallen asleep with a party hat and doughnuts?

It's from season 6, episode 8. "Invest in Love" Callie had a surprise party for Arizona's birthday, but Arizona didn't stay for it cause she had just Lost a patient. Callie fell asleep waiting for her. It was also the first time Arizona told Callie she loved her. Awesome scene.

they were celebrating their "I Amore YOU's"