Php addition removes all styling

I’m using the following code to call subcategories when on category pages.

<?php
if ( is_category() ) {
$current_cat = get_query_var(‘cat’);
wp_list_categories(‘&title_li=&show_count=1&child_of=’.$current_cat);
}
?>

The problem is using this removes all styling and content besides the echoed subcategories.