Dress code for females in Iran is not really specific and defined. You can wear different kind of clothes as tourist and it would be acceptable as long as Hijab is somehow observed. I did a Google search to find some pictures which hopefully will be helpful. I tried to pick out those kinds that you may have got or can easily get from where you live, so that you won't have to waste your time to get the suitable Mantuea in Iran. You may consider the size and the style of these blouse and shirts are acceptable as long as they go with long pants and scarves. Some of them are those you usually wear with leggings but they must be worn with pants here.
Female tourist in Iran has to cover their hair appropriately. They should also wear loose fitting garments which cover arms and legs up to at least the knee area over pants or skirt with a scarf in summer, and a full-length woolen coat and scarf in winter (calf-length is acceptable if worn over pants).
Dress attire for men is similar to that in Europe. The strict dress code for men in Iran prohibits short trousers and short sleeved shirts and t-shirts. Although you would not see Iranian men dressed in shorts, you will almost certainly see men wearing short sleeved shirts and t-shirts.
Sandals and flip flops without socks is acceptable for both genders and makes no problem.