Styrofoam is perfectly safe for eating and drinking food and drinks from and no harm will be caused to you and your health.
However if you heat food up in Styrofoam containers and it melts into the food then that could cause health concerns if you eat the food.
But heating some food in Styrofoam in the microwave is fine and nothing bad will happen to you as a result.
Styrofoam is used everyday for holding drinks such as soft drinks, tea, coffee etc and no one has gotten sick as a result and if the Styrofoam were to be found unsafe for us then the health departments wouldn't allow the Styrofoam to be used to serve food and drinks with.