I don't know if it looks as you intended on your side, but on my end it seems a bit screwy. The snow starts on the far left of the page, but doesn't make it all the way across. It's like it's the width of the main part of the page, but not overlapping it quite right. However, that might be a good thing, because it seems having a snow GIF on top of things prevents anything below from being clicked--I couldn't even click on your Message Wall link to say this stuff. Sorry to say I have no tips for making it work better, though.
I think I see why the difference in how it looks. I'm guessing you generally use the mobile version of the site? Seems the code basically says "Take this full other page, show it on top of this one". Since with the mobile site the content generally takes up the entire width, everything completely overlaps. With the desktop site there are bars at the side where only the background is shown, plus some other navigational stuff on the right side, so things just don't line up as well. Probably some way to make that work better, but I couldn't say how right now.
I did find the trick to make it possible to click or select things underneath, though; adding ;pointer-events:none to the div style section.