Html version shows lines around folded corners

[btzr-io]

[musaticsgilbert]

To give further information: this happens only in Firefox. Something differs in the Firefox and Chrome renderers which causes the weird glitch. (Also, on another note, the folding also makes the size of the div bigger because of the transformation which can make the sidebar appear and cause scrolling issues if you scroll down while the sidebar is on. You can try it on a simple page with only the book inside and scroll while your cursor is inside the folding area. I'm aware that this might be a sacrifice for the div reaching outside of the div area and I can turn it down by setting the overflow on the container to hidden but authenticity goes with it too which can bee important with visual libraries like this).