Bing has updated the Bing Webmaster Tools design as of a couple days ago. The new design isn't that much different from the old one but the icons, layouts and some of the report design have all been updated.
Glenn said this is "more cosmetic than anything else." The WebmasterWorld moderator said the "icons & viewport are more mobile friendly," although they are not responsive. He added:
For example, on Dashboard the older up & down icons were either red or green arrows inside circles. Now they are just the colored arrows askew.
Besides the new icons, all the graphs & reports have a new, HTML5 look and the presentation is more mobile friendly than it was, although not responsive.
Here are screen shots of the new design:
You can see the old version in this Search Engine Land article for not too long ago.