tinternet.net/core/Resources/views/site/node_admin/new.html.twig

<div class="modal-dialog">
    <div class="modal-content">
        <div class="modal-header">
            <h5 class="modal-title">
                {{ 'New element'|trans }}
            </h5>
            <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                <span aria-hidden="true">&times;</span>
            </button>
        </div>
        <div class="modal-body">
            <form action="{{ path('admin_site_node_new', {node: node.id}) }}" id="form-node-new" method="POST">
                {{ include('@Core/site/node_admin/_form.html.twig') }}
            </form>
        </div>
        <div class="modal-footer">
            <button type="button" class="btn btn-secondary" data-dismiss="modal">{{ 'Cancel'|trans }}</button>
            <button type="submit" form="form-node-new" class="btn btn-primary">{{ 'Save'|trans }}</button>
        </div>
    </div>
</div>