Background blocks in parallax doesn't work when they are full-sized

[jebin]

I have a problem with my parralax. When I try some parralax background tutorial, they doesn't work fine in high-resolution. So I use this css background-size: cover;Then the background occuped the whole space of my screen but there are enormous space between each background when I resize my windows in some resolution (like 4:3 resolution). And I don't know why ?I use a tutorial of alsacreation.com to show you the problem:http://lory-huz.fr/parralax/Try to resize the window and you will see these space.