Thanks Tom, your code to add class works fine.
I hope you don’t laugh at me but I’m not a developer:) I did this and only the word “Array” returns to me.
$terms = get_terms( ( array('taxonomy' => 'post_tag', 'hide_empty' => false,)));
if ( isset( $terms ) && '' !== $terms ) {
echo '<div class="tax referencia">';
echo $terms;
echo '</div>';
}Can you help me with taxonomies, please?