One of the new features in macOS Sierra is Picture in Picture multitasking. When watching a video in Safari or iTunes you can now float that video over the desktop so you can continue working on other things. The floating video screen can be pinned to any corner of you Mac’s screen and resized.
Sometimes, having the video pinned to one of the corners of the screen might be inconvenient. Luckily there’s an easy way to move it around and place it exactly where you want.
When floating a video from YouTube ( for example ) hold down CMD and then drag the video screen to the position you desire. It’s that easy. Enjoy!