That's almost always because hardware acceleration is off in your browser. Open the help tab for the two-minute fix.
This installation is built with 3D graphics that need your browser's hardware (or "graphics") acceleration turned on. It's on by default in most browsers — if this piece won't load, that setting has probably been switched off.
Test whether your browser supports this →
If the piece didn't fill your screen automatically, your browser may have blocked the fullscreen request — press F11 (Windows) or Ctrl + Cmd + F (Mac) to toggle it yourself.