Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
John Ive's "very, very flat" design for iOS 7
Recent reports suggest Ive has chosen to strip iOS 7 of “all signs of gloss, shine and skeuomorphism”. John Ive comments on his thoughts and ideas for the new operating system.
Ive’s control of all user interface has been dominant since last October. In his new position, he comments on the new upgrade as “surprising” but insists there will still be “no new learning curve”. He quotes that the “core apps and system fundamentals” will stay the same, in reference to the home & lock screen and Apple’s own Apps like Notes. However, iOS 7 is expected to bring a whole new icon set for Apple’s homemade apps, as well as a improved design to tabs and tool bars.
We expect that Apple want to give the new iOS a new look and feel, yet still keeping it as simple as possible. An element that has been popular in apps like Flipboard offer an improved swipe based gestures and we are looking into seeing this same feature on iOS 7, much like the Notification Center that we saw released back in iOS 5.