Unfortunately, with this version of Ren’Py 8.4.0 the screen goes black in the web version when trying to play online in full screen. I looked it up and it seems to be a bug in this Ren’Py release. For the next update I’ll try using an older version of Ren’Py so it can be played in fullscreen on the web. If you want to play in fullscreen for now, you’ll have to download the game. Sorry for the inconvenience!