How do I have the exit button become visible after the curtain is up?

https://jsfiddle.net/96fm3rhv/4/

window.onload = function() {
  const container = document.querySelector(".video-containerA");
  const spinner = document.querySelector(".spinner");
  const exitButton = document.querySelector(".exitA");
  
  spinner.addEventListener("animationend", function() {
    container.classList.add("slide");
  });
  container.addEventListener("animationend", function() {
    exitButton.classList.add("visible");
  });
};