Add span to archive post count
wp_get_archives() itself doesn't have any useful filters we can hook in to, but get_archives_link() (which it calls and passes the post count output to) does.
You can use an almost identical function and hook it to the get_archives_link filter:
function so_40551791_style_the_archive_count($links) { $links = str_replace('</a> (', '</a> <span class="archiveCount">(', $links); $links = str_replace(')', ')</span>', $links); return $links;}add_filter('get_archives_link', 'so_40551791_style_the_archive_count');Note, the where there was a space before.