Zài yúyuè de fēnwéi zhōng, dàjiā liáo de hěn kāixīn.
In the pleasant atmosphere, everyone chatted happily.
Tips
register
愉悦 is more literary and formal than 高兴 (gāoxìng, happy) or 开心 (kāixīn, glad). It's common in written Chinese and formal speech, less so in casual conversation.
grammar
愉悦 can function as both an adjective (愉悦的心情, a joyful mood) and a verb (愉悦身心, to delight body and mind).
