Thank you for your message, I hope you are doing well. You can certainly customize your notifications, however there are some limitations when doing so.
I recommend checking out our Editing notification templates guide where it walks you through how to edit your notification colors. It also walks you through all available customizations you can make within your notification templates.
Fonts are not something you are able to change natively within your notification customization area. This could be something a developer or a Shopify Expert could take a look into potentially customizing.
I hope this information helps you out moving forward. Let us know if you have any additional questions, we are always happy to chat!