I'm looking into the various solutions to make a site work on both desktop and mobile platforms and understand from reading about it that the most failsafe solution is to have it automatically rearranges itself depending on the screen size.
A neat example I came across which does this is Creattica.

I'm trying to learn more CSS but could someone please explain to me the general concept of how the mentioned site does this? It works without Javascript, but it won't even let you in with cookes disabled so I'm wondering if that has anything to do with it or if it's all in CSS.