Changing Background Image Size (Classic Example)

[newbie5402]

Hi! This question probably has an easy fix, though I can't quite find the solution.

Following prinzhorn's "classic example" of skrollr, I am attempting to change all the parallax background images to a height that is 60% of the viewport. In the classic example, the images sizes are either full screen (100% height) or 50% height.

I have tried tinkering with the following classes, in addition to the CSS translate3D property for the fixed images: .parallax-image-wrapper-## .parallax-image-## .gap-##

Any help would be greatly appreciated!