nineskeletor/src/Form/WhitelistType.php

<?php

namespace App\Form;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\SubmitType;
use Symfony\Component\Form\Extension\Core\Type\TextType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;

class WhitelistType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('submit',
            SubmitType::class, [
                'label' => 'Valider',
                'attr' => ['class' => 'btn btn-success'],
            ]
        );

        $builder->add('label',
            TextType::class, [
                'label' => 'Label',
            ]
        );
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults([
            'data_class' => 'App\Entity\Whitelist',
            'mode' => 'string',
        ]);
    }
}