Why do we say "BuenOS dias", "BuenAS tardes", "BuenAS noches"

Why do we say “BuenOS dias”, “BuenAS tardes”, “BuenAS noches” ? Is “dias” a masculine word and “tardes”/“noches” feminine ?

1 Like

Yes, exactly.

El día, la tarde, la noche.

Aah, ok, many thanks.