A JavaScript focused window could overlap the fullscreen notification in Fullscreen in Google Chrome prior to 66.0.3359.117 allowed a remote attacker to obscure the full screen warning via a crafted HTML page.
https://access.redhat.com/errata/RHSA-2018:1195
https://chromereleases.googleblog.com/2018/04/stable-channel-update-for-desktop.html