How to scroll a modal window on Bootstrap ?

I have a site with Drupal 8 and Bootstrap 3

I created a custom module to display a page in a modal window. The page contains a lot of text and I want it to have a scrollbar on the modal window.

How can I do this ? Here is the code of my module and the information I found :

https://getbootstrap.com/docs/4.3/components/modal/#scrolling-long-content

You can also create a scrollable modal that allows scroll the modal
body by adding .modal-dialog-scrollable to .modal-dialog.

I do not even know if my code is correct for Bootstrap or if it can be improved.

<?php
 
namespace Drupal\commerce_marketplace_terms_and_conditions\Plugin\Commerce\CheckoutPane;
 
use Drupal\Component\Serialization\Json;
use Drupal\Core\Form\FormStateInterface;
use Drupal\commerce_checkout\Plugin\Commerce\CheckoutPane\CheckoutPaneBase;
use Drupal\commerce_checkout\Plugin\Commerce\CheckoutPane\CheckoutPaneInterface;
use Drupal\Core\Link;
use Drupal\Core\Url;
 
/**
* Provides the completion message pane.
*
* @CommerceCheckoutPane(
* id = "marketplace_terms_and_conditions",
* label = @Translation("Marketplace Terms and Conditions"),
* default_step = "review",
* )
*/
class MarketplaceTermsAndConditions extends CheckoutPaneBase implements CheckoutPaneInterface {
 
/**
* {@inheritdoc}
*/
public function buildPaneForm(array $pane_form, FormStateInterface $form_state, array &$complete_form) {
$store_name = $this->order->getStore()->getName();
$store_id = $this->order->getStoreId();
$pane_form['#attached']['library'][] = 'core/drupal.dialog.ajax';
$attributes = [
'attributes' => [
'class' => 'use-ajax',
'data-dialog-type' => 'modal',
'data-dialog-options' => Json::encode([
'width' => 'auto'
]),
],
];
$link = Link::fromTextAndUrl(
$this->t('terms and conditions of the store "@store_name"', ['@store_name' => $store_name]),
Url::fromUri("internal:/store/$store_id/cgv", $attributes)
)->toString();
$pane_form['marketplace_terms_and_conditions'] = [
'#type' => 'checkbox',
'#default_value' => FALSE,
'#title' => $this->t('I have read and accept @terms.', ['@terms' => $link]),
'#required' => TRUE,
'#weight' => $this->getWeight(),
];
return $pane_form;
}
 
}

[![enter image description here][1]][1]

  [1]: https://i.stack.imgur.com/Jc5Xr.png