"στη γιορτή" instead "στην γιορτή". "Βράδι" should also be accepted as correct. Most vocabularies have it as a secondary writing of "Βράδυ=night".
Yes, we'll correct the στη /στην issue in the new tree it's at the top of the "to do" list. We also include "το βράδυ" as another form of tonight.