Flowers are flying everywhere in the spring city, and the east wind is cold and the willows are oblique. What festival is it about?

The poem you are talking about was written by Han Yi, a poet in the Tang Dynasty. Described the related situation of the Cold Food Festival. I will give you the relevant explanation:

An outdated festival (Qingming Festival) that started one or two days ago in Tomb-Sweeping Day, when only cold food is served for three days.

[Tang] Han Yi

Spring city is full of flowers,

Cold food, Dongfeng willow, xiá.

At sunset, in the Han Palace, people distribute candles.

Light smoke scattered into the Five Emperors Hall.

Cold Food Festival: A traditional festival in ancient times, which lasts for one or two days in Tomb-Sweeping Day. From this day on, the ancients did not make a fire to cook for three days, so it was called cold food.

In Chang 'an in late spring, catkins are flying all over the sky. Cold food festival, the wind blows the branches of the imperial garden. As night falls, the palace is busy distributing candles, and the smoke from the kitchen chimney is scattered into the homes of princes and nobles.

[Appreciation of Works] This is a poem describing the scene of the Cold Food Festival. The poem first describes the scene of Chang 'an in spring: late spring is approaching, and the whole city is full of tidbits and smells of spring. Then take a scenery from this infinite landscape to describe it in detail: during the Cold Food Festival, the east wind blew and the willow branches in the imperial garden fluttered with the wind. Then it focuses on a special landscape in the palace: night arrival, all over the world, every household.

Please refer to it, please adopt it if you are satisfied, thank you!