We've added a site builder with WYSIWYG editing to the Checkout Upsell and Cross-sell editing experience. 

This update enables merchants to edit their text directly in real-time, removing the need to switch between input and preview modes. It improves consistency across our Flows offering, and makes customizing faster and more intuitive.

See our documentation for more information on customizing your Checkout Upsell and Checkout Cross-sell experiences.