The game is incredibly buggy for me: the first few times, I found that clicking the fullscreen arrows in the lower right caused the game to (permanently, until reloading the page) lose focus; clicking on it did nothing. Then, by ignoring the arrows, I was able to click on the "play" button on the level select screen, which caused it to start flickering between level-select and title screens. Now, when I reload the page and click "run game", it's just black.
I suspect this is all details of Unity and not really a deep-seated flaw in the game, which means it's hopefully easy to clear up!