Just show a blank fullscreen.
Click the "Enter fullscreen" button above to enter blank screen
Enter/exit fullscreen by double clicking in page blank area. Show/hide mouse cursor by holding Ctrl/command key and double clicking on page.
Note for macOS Safari users: due to an issue of Safari, to hide mouse cursor without distraction you may need to press ⌃⌘F or 🌐F to put window in fullscreen mode, then click "hide mouse cursor" manually.
Settings: set background to "black", check "Keep screen awake"
Settings: set background to "bright"
Settings: set background to "chroma key"
See README for more details.