Fixing the text

I have a page where we sell propane. Pilots who purchase the propane pay by the 100th of a gallon. For example after a flight a pilot may have used 24.15 gallons. We have an app set up that will allow us to charge for portions of a gallon. The issue I am having is the text format for the page. I would like to customize it a little but I am unsure how to go about it.

https://aviation-ranch.com/support/Customizing-product-text.png

The image above is what i am looking at and trying to figure out the custom code to add to my Appearance>customize>customcode section in the admin area.

Any help or tips would be great. I would love for someone to explain where everyone gets the code from. By inspecting the source I can see parts of the code but I do not understand how to get all of it.

Thank you.
Jeff (the 65 year old newbie)

The page I need help with: [log in to see the link]