Why does my tool bar (date, etc) appear when watching videos in full screen mode

[fitterhappier]

When I watch videos, either on Youtube or elsewhere, my toolbar, if that's the right word, the one that includes my battery life, wifi strength, date, time, etc, is a contant fixture even if the video is in full screen mode.

How do I remove the toolbar when I watch videos in full screen mode?

Thanks.