Each parallax container takes a CSS class for direction relative to scrolling — with or against — and a speed rate
<div class="parallax-group">
<div class="parallax-container background against" data-rate=".5"></div>
<div class="parallax-container foreground against" data-rate=".75">...</div>
<div class="parallax-container foreground with" data-rate=".5">...</div>
</div>
<div class="parallax-group">
<div class="parallax-container background with" data-rate=".25"></div>
<div class="parallax-container foreground against" data-rate=".25">...</div>
</div>
<div class="parallax-group">
<div class="parallax-container background against" data-rate="1"></div>
<div class="parallax-container foreground with" data-rate=".5">...</div>
<div class="parallax-container foreground with" data-rate=".25">...</div>
</div>