happy-go-lucky --------- 无忧无虑的（形容词，非正式）

英文释义
(adjective, INFORMAL) Describing a cheerful, carefree person who has a relaxed, unconcerned attitude about everything.

例句
While my aunt is a serious woman who seldom laughs, my uncle is a happy-go-lucky man who never worries about the future.
我的婶婶是个严肃的人，很少大笑，而我的叔叔是个乐天派，从不担心未来的事情。