Background getting bigger

Hello,

First of all, thanks to the creator of this plugin. It was really important to me to be able to publish my story and I was horrified when I discovered WordPress couldn’t handle it.

The text of my project looks fine. My problem is : the background, which is ok in the first passage, gets bigger each time you go to annother passage. The consequences are :
– my background image either is more and more deformed, or a part of it each time bigger is off the iframe (at the bottom and on the right).
– the reader need to scroll more and more to access the buttons I fixed at the bottom of the screen.

When I tested my project without wordpress, nothing special happended with this background-image. I don’t know if I should correct something in my Twine project or in my WordPress page builder.
I would be grateful if any of you have an idea.

PS : If you want to test my link, you need to know my project is made for mobile devices. Indeed I put some Javascript so that you can navigate from a passage to the next by swiping to the left. Only passages with orange triangles in the background use the “normal” mode of Twine, meaning clicking among choices.
I don’t think it interfere with my background probleme, because this problem of background getting bigger happends in every passages, whenever you swipe or you click.

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