No. Body fluids such as urine, tears, and sweat are typically acellular, meaning there are no cells present. The concern would be if there were red blood cells. Assuming the urine on the toilet seat was nonbloody, you are at no risk for getting HIV on a toilet seat. In fact, even if the urine was bloody, your intact skin is a good enough barrier against HIV infection. No worries!
No. Hiv, the virus that causes aids, is transmitted via blood, semen, vaginal fluids, and breast milk. There have been no documented cases of HIV contraction from urine, sweat, and saliva.