@media (max-width: 550px) {
  #loginForm,
  #registerForm {
    width: 300px;
  }
  h1 {
    font-size: 25px;
  }
}

@media (max-width: 400px) {
  #loginForm,
  #registerForm {
    width: 280px;
  }
  h1 {
    font-size: 20px;
  }
  p {
    font-size: 14px;
  }
}