Here is your code, from what I can see it seems to be completely working. All I did here was add a button to toggle the hidden
class.
function toggleHiddenClass(){ document.querySelector('#gameOverMessage').classList.toggle('hidden'); }
#gameOverMessage { z-index: 1; text-align: center; position: relative; font-size: 150px; color:rgb(235, 28, 28); font-weight: bold; } .hidden { display: none; }
<button type="button" onclick="toggleHiddenClass()">toggle hidden class</button> <div id="gameOverMessage" class="hidden"> Game Over! </div>