Very casual... but still dress nice! I wore jeans and a nice top. The interview process did not take long. I think my interview lasted about 10 mins and they let you know right away if you are hired.

large interview groups, everyone sat in the same room and waited to be called in. multiple interviews were conducted at the same time in the same room. not very professional. the overall experience was nerve racking because of the initial feelings of nervousness (large number of applicants gathered in one room).