form {
  width: 100%;
  max-width: 300px;
  margin: 0 auto;
  color: midnightblue;
}

form button[type='submit'] {
  display: block;
  margin: 0 0 0 auto;
}

@media (min-width: 768px) {
  form {
    margin: 0 0 0 20px;
  }
}