nonchalant

Despite the accident, he maintained a nonchalant attitude, as if nothing had happened.

(Chinese) 尽管发生了意外，他依然保持着若无其事的态度，仿佛什么都没发生过。

She gave a nonchalant shrug when asked why she was late for the meeting.

(Chinese) 当被问及为什么开会迟到时，她若无其事地耸了耸肩。