adjective
festive
FES-tiv/ˈfestɪv/
Suited to or expressing joyful celebration.
The women raise glasses beside a festive cake and flowers.

Etymology
From festum, “holiday,” festive moved from “pertaining to a feast” to the cheerful mood associated with celebration. Its modern English use may be a back-formation from festivity.
In context
we are to strew the city with flowers and Adorn it as for a festive celebration