How to remove the parentheses from the category widget

Add this code to your functions.php file and it will remove the parentheses and surround the post count with a span with a class to easily style it.

function categories_postcount_filter ($variable) {
   $variable = str_replace('(', '<span class="post_count"> ', $variable);
   $variable = str_replace(')', ' </span>', $variable);
   return $variable;
}
add_filter('wp_list_categories','categories_postcount_filter');

++Bonus
In the archive widget, if you checked “Show posts count” checkbox you’ll see the same parentheses around posts count, here’s another filter to remove them and add a class to easily style theme.

function archive_postcount_filter ($variable) {
   $variable = str_replace('(', ' ', $variable);
   $variable = str_replace(')', ' ', $variable);
   return $variable;
}
add_filter('get_archives_link', 'archive_postcount_filter');