3D FlipBook - Avoid controls overlay

Cheers, here's a pic to help you visualize my problem: https://i.imgur.com/ardqpHm.jpg.

Left is how the plugin works by default, right is what I need. Basically I'd like the book canvas to occupy a fixed percentage of the view container's height (let's say 85%), and the controls div to fill the remaining part. I've tried tinkering with the css a bit but it looks like the canvas size is dynamically calculated through js rather than via css. Is it correct? Do you think it is possible to achieve what I have in mind? If so... could you suggest me the file that I'd have to modify?

Thank you in advance.