How to spot the layout errors on a copied site

Hello. I have two sites, one french, one english and I’d like the layouts to be the same.

I briefly flirted with Moesia as a theme, and then swapped back to Aletheia, because I found a way to get the header image to be responsive (YAY!)

So when I copied the exact same CSS from this site, into my site here, the main body is “stuck” under the header image and there’s no clever scroll effect.

Anyone care to help me play “SPOT THE DIFFERENCE?”