Nino Bilic provides the cool images and css for the OWA XBOX theme in a recent entry on the Exchange blog. Back in early 2003 when we were finishing up development on the product and many mailboxes at Microsoft were dogfooding our bits, OWA dev decided to show off the feature on April 1st. The dev building the feature came up with a Hello Kitty theme and arranged to change the default theme on everyone's mailboxes to the new Hello Kitty one, then segmented out Themes as a feature. The effect was that everyone had Hello Kitty UI and couldn't change it. We're so funny.