Chrome Version       : 71.0.3578.98
OS: Mac OS X

What steps will reproduce the problem?
1. Go to https://googlechrome.github.io/samples/picture-in-picture/
2. Click "Toggle Picture-in-Picture" button
3. Click Picture-in-Picture window and press <Tab> key multiple times

What is the expected result?
I should navigate through Picture-in-Picture window controls

What happens instead of that?
Nothing.

There are no blue (or orange) outline rectangles as well that I can see in Chrome OS, Linux, and Windows.