Good night
The Italian phrase 'Buonanotte' is used similarly to the English 'Good night'. It is typically said as a farewell in the evening or before going to sleep. Just like in English, it can also be used as a salutation in a written communication like a letter or an email.
Goodnight, I hope you have nice dreams
This phrase could be used when wishing someone, probably someone close to you like a family member, a peaceful night and pleasant dreams.
Tonight is a quiet evening, goodnight
This is a phrase someone might use to comment on the peacefulness of the evening while concurrently wishing someone goodnight.
Goodnight, see you tomorrow
This phrase is typically used to convey a casual farewell to someone, indicating that you intend to see them on the following day.