Improve native form validation handling

[robsonsobral]

  /* old browsers */
  &:invalid {
    /* Invalid input UI styles */    
  }

  &:valid {
    /* Valid input UI styles */    
  }

  @supports selector(:user-invalid) {
    &:invalid {
      /* override old browsers styles */
      /* Valid input UI styles */
    }

    &:user-invalid {
      /* Invalid input UI styles */
    }

    &:user-valid {
      /* Valid input UI styles */
    }
  }