This website template is completely mobile-friendly and only uses HTML-v4 and CSS-v2, meaning it is compatible with nearly all browsers and devices, including those which are several years out of date! No javascript is needed at all. The effect is achieved by including semi-transparent foreground images over the top of the content which is allowed to scroll independently of the theme elements.
Any sort of content can be included behind the curtain, provided it does not override the z-index of the content area which keeps it hidden behind the curtain when the page loads.