the translation for great is "grandioso" so you can say "Que tengas un grandioso día" but is not common to say it. The most common is to can say: "Que tengas un excelente día"
¡Sí, día! in Spanish is "Yes, day!" in English.
"Que dia es?"
"nuevo dia"
¿Cómo fue tu día?
The phrase "buen día" translates to "good day" in English.
This expression means a bad day.
How is your day going can be translated from English to Spanish as como va su dia. This can be used as a greeting.
27 good day/morning 27
Feliz Día de San Valentín
La siesta is the time of day when mystery and unilateralism become one
Spero sia una Bella giornata.
That's Spanish, and it means: "One day to build his walls".