commerce-8.x-2.8/modules/checkout/templates/commerce-checkout-form.html.twig

{#
/**
 * @file
 * Two column template for the checkout form.
 *
 * Available variables:
 * - form: The form.
 *
 * @ingroup themeable
 */
#}
<div class="layout-checkout-form clearfix">
  {{ form }}
</div>