Problem: The two cards next to the lion will appear in fullscreen mode: https://i.imgur.com/aZSHD7C.jpg Steps to reproduce: - Open: https://nextendweb.com/bug/webkit/showcase/?a - Click on the lion image with play button - YouTube video starts to play, click on the full screen button Happens in: Safari 11.1.2 Safari Tech Preview 12.1
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