How can I change the options font and style?

In the App on the Live Product Options page, open a configuration and

watch the following video to learn how to change the design of the product options:

The default font is set to the most common fonts that are widely available on most devices.

You can enter the font name that is used in your theme. If the font contains a space, make sure to wrap the name in single quotes:

Important: The app does not automatically load the provided font name, you have to make sure that the font is loaded in your theme.

Please visit the official Shopify theme guide on how to edit your theme typography.