Question: A bunch of sites, such as <http://scaleofuniverse.com/>, have zoomable interfaces that will allow you to "zoom through" items to reveal "smaller" items contained within them. I have always seen this done in Flash, but am wondering how it could be made using JavaScript and CSS. Is there any open-source library out there that supports this feature?

Also, I have had a look at impress.js, which has some very cool features, but I am unsure whether I would be able to accomplish the desired effect using this library. Is it just a matter of using the right CSS styles?

Answer: 
The process is very complex but its doable, here is a great article on how to come up about it, [Create a zoomable user interface with CSS3](http://www.netmagazine.com/tutorials/create-zoomable-user-interface), and also a jQuery plugin that provides a close effect that you are looking for, [Zoomooz](http://janne.aukia.com/zoomooz/).
If you the interface element is an HTML element, you could expand the element until it fills the screen, whilst at the same time fading the opacity down to 0. This technique would depend on any images used in the interface element being scalable (possibly use `background-size: cover`).

You could use css transitions or javascript to achieve the effect.