"Have a good evening!"
Translation:Bonne soirée !
Bonsoir simply means "good evening" and can either be a greeting or a way of saying goodbye. Although it can be used in either a formal or informal situation, you are more likely to hear it in formal circumstances.
Bonne soirée also literally translates to "good evening," but is only used when leaving someone because you are actively wishing them enjoyment for the rest of the evening. The phrase means "have a good evening" instead of just the "good evening" suggested by a literal translation.
Bonsoir is good evening as a greeting. Bonne soirée is feminine because it is talking about the time. Have a good time/evening. When you are literally talking about the time, it becomes feminine.
Bonjour is a greeting, but bonne journée means have a nice time/day. Greeting = masculine. Telling time = feminine.
Linguee also gives 'passez une bonne soirée' which is idiomatically more familiar to a native Englsih speaker.