“Tznius is about the person him/herself not about who they are dressed in front of.”
it’s both. there are two concepts in tznius. 1) in front of others (which applies more/mostly to women)and the shayla once came up if girls can go swimming near a guest house that was being built by goyim (and they could see in a little) and it was – assur. 2) in front of Hashem. In front of yourself