View file modules/guestbook/templates/result.phtml

<?php $this->layout('system::layout/default', [
    'title'      => $title,
    'page_title' => $title,
]) ?>
<div class="row">
    <div class="m-sm-auto m-md-auto m-lg-0 col-sm-8 col-md-8 col-lg-7 col-xl-8">
        <div class="card shadow border-0 border-radius-12">
            <div class="card-body">
                <h4 class="card-title"><?= $title ?></h4>
                <?= $this->fetch('system::app/alert', [
                    'alert_type' => $type == 'success' ? 'alert-success' : 'alert-danger',
                    'alert'      => $message,
                ]) ?>
                <?php if (! empty($back_url)): ?>
                    <a href="<?= $back_url ?>" class="btn btn-primary"><?= __('Back') ?></a>
                <?php endif; ?>
            </div>
        </div>
    </div>
</div>