Hi rrafal889,

Thanks for reaching to us.

Go to Theme Settings > Typography > Advanced. In this area, you can assign elements to below Custom Class

span.wc-price-history.prior-price-value

Please refer to our documentation https://xtemos.com/docs-topic/advanced-typography-settings/

Regarding price’s font-size, you are using a Custom Single Product layout, which is built with WoodMart WooCommerce builder. Navigate to Layouts > Layout to edit Single product layouts > select price widget and change font-size.

Further, you can read more about the Layout Builder here: https://xtemos.com/docs-topic/woodmart-woocommerce-layout-builder/

Regards,