Desktop, actually. Full HD. The width of the content is only 800px, but some of your images (like diagram2.png) is 1044px wide. And instead of the image being scaled, it is just being cut off.

Edit: Oh yea, there we go. You're using CSS zoom[0], which is non-standard.

[0] https://developer.mozilla.org/en-US/docs/Web/CSS/zoom