"We used this as an opportunity to really push what Dan has been calling "progressive enrichment": sprinkling in some modern CSS declarations even if not every browser gets all of them [...] So if you view the UX London site in IE6 it looks fine. Nothing special though. But if you view the site in a browser like Safari, a lot of little details shine through. The design is pretty much a test-case for the box-shadow property using RGBa."