FormTestButtonClassForm.php

<?php

namespace Drupal\form_test\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Builds a simple form to test form button classes.
 *
 * @internal
 */
class FormTestButtonClassForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'form_test_button_class';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form['button'] = [
            '#type' => 'button',
            '#value' => 'test',
            '#button_type' => 'foo',
        ];
        $form['delete'] = [
            '#type' => 'button',
            '#value' => 'Delete',
            '#button_type' => 'danger',
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
    }

}