If you are casual, you are, or you pretend to be, relaxed and not very concerned about what is happening or what you are doing.
It's difficult for me to be casual about anything.
要我轻松待事有难度。
A casual event or situation happens by chance or without planning.
What you mean as a casual remark could be misinterpreted.
你不经意所说的话可能会被误解。
Casual clothes are ones that you normally wear at home or on holiday, and not on formal occasions.
I also bought some casual clothes for the weekend.
我还买了些休闲服准备周末穿。