dsfr4drupal-1.x-dev/templates/form/horizontal-tabs.html.twig

<div data-horizontal-tabs class="horizontal-tabs">
  <div class="fr-tabs"></div>
  {# Cannot add list into "fr-tabs", otherwise it's not populated. #}
  <ul data-horizontal-tabs-list class="horizontal-tabs-list fr-tabs__list"></ul>
  <div data-horizontal-tabs-panes{{ attributes }}>{{ children }}</div>
</div>