fonksiyona ekle
<ul>
    <?php wp_list_categories( array(
        'title_li' => '<li class="list-group-item">' . __( 'Poetry', 'textdomain' ) . '</li>'
    ) ); ?> 
</ul>

böyle kullan
<ul class="list-group">
<?php wp_list_categories(); ?>
</ul>