What to wear to outdoor concert/opera in Venice?

We will be attending the outdoor Andrea Bocelli concert in Venice's St. Mark's square and have no idea what to wear! I haven't had much luck searching the internet and don't know if the same dress as an indoor opera is necessary. Any help would be appreciated!

The Italians like to dress up, so you wouldn't be overdressed if you showed up in formal dress. But since I assume you're on holidays, I wouldn't bother in your case. No-one will frown on you for not wearing an evening gown