An 'onlooker' is a nonparticipating observer; a spectator. The word 'onlooker' is a noun, a word for a person.
bystander - onlooker
it means: "that person is casual".
It is a mix between the casual and sophisticated look...
casual
formal means to be casual and not so important just for taste
Dressing casual means slacks and a dress shirt and nicer shoes.
casual observation
Yes, both a witness and an onlooker are the same thing, one who sees an event unfold.
What do you mean............ she is a singer, doing the casual.
casual chat
A casual woman.