Category post navigation with toggle-able detail

cat-post-nav.php

<?php
// List all categories with detail of posts in categories
function list_categories_with_posts() {

    $categories = get_categories();
    $output = '';
    $current_post_id = get_the_ID();

    foreach ($categories as $category) {
        // Print toggle-able detail element for each category
        $output .= '<div class="category-navigation"><details>';
        $output .= '<summary>' . $category->name . '</summary>';

        // set our query args
        $args = array(
            'category__in' => array($category->term_id),
            'post_type' => 'post',
            'posts_per_page' => -1,
        );

        $posts = new WP_Query($args);

        // get posts within category
        if ($posts->have_posts()) {
            $output .= '<ul>';

            while ($posts->have_posts()) {
                $posts->the_post();

                // Check if the current post matches the related post
                $current_class = ($current_post_id === get_the_ID()) ? 'current-post' : '';
                $output .= '<li class="' . $current_class . '"><a href="' . get_permalink() . '">' . get_the_title() . '</a></li>';
            }

            $output .= '</ul>';
        }

        $output .= '</details></div>';
    }

    // Reset the post data
    wp_reset_postdata();

    return $output;
}

add_shortcode('category_posts', 'list_categories_with_posts');