Hello Jun,
Due to the WordPress standards as well as data validation issues, widget short description doesn’t support HTML tags. So, if the widget doesn’t support html tags, you need to remove esc_html from the code.
Please find the codes on acmethemes/sidebar-widget/acme-featured.php line 162. <p><?php echo esc_html( $sub_title ); ?></p> Remove exc_html from the code there and try once by adding the HTML tags.
Hope this will solve your problem.
Regards