Hi George,

#1. Please add below CSS code to WP-Admin → Appearance → Customize → Additional CSS:

.woobt-summary .woobt-additional {
    color: #DD3333;
    font-size: 20px;
}

.woobt-summary .woobt-total {
    color: #1e73be;
     font-size: 20px;
    font-weight: 700;
}

And the result:

You can change the font size or color in the CSS code above to whatever you want.

#2. Please add the custom code below. (How to add custom code? ↗):

add_action( 'wp_footer', function () {
	?>
    <script type="text/javascript">
      (function($) {
        $(document).on('woobt_calc_price', function(e, total, total_ori, total_ori_regular, $wrap) {
          var $products = $wrap.find('.woobt-products');
          var ori_price_suffix = $products.attr('data-product-price-suffix');

          if (total === 0) {
            $wrap.find('.woobt-total').html(woobt_vars.total_price_text + ' ' +
                woobt_price_html(total_ori_regular, total_ori) + ori_price_suffix).slideDown();
          }
        });
      })(jQuery);
    </script>
	<?php
}, 99 );