mercury_editor-2.0.x-dev/components/component-outline-region/component-outline-region.twig

<div class="me-component-outline__region-controls"> {% block prefix %}{% endblock %}
  <span class="me-component-outline__region-label">
    {{ item.label }}
  </span>
  {{ addButton }}
  {% block suffix %}{% endblock %}
</div>