link_inside_archive_and_category_widget.php

<?php 

/* This code filters the Categories archive widget to include the post count inside the link */
add_filter('wp_list_categories', 'cat_count_span');
function cat_count_span($links) {
    $links = str_replace('</a> (', ' <span class="count">(', $links);
    $links = str_replace(')', ')</span></a>', $links);
    return $links;
}

/* This code filters the Archive widget to include the post count inside the link */
add_filter('get_archives_link', 'archive_count_span');
function archive_count_span($links) {
    $links = str_replace('</a>&nbsp;(', ' <span class="count">(', $links);
    $links = str_replace(')', ')</span></a>', $links);
    return $links;
}