我正在YouTube上观看一个项目的视频，一个简单的石头剪刀布游戏。根据我已经完成的，我应该可以点击让我们玩按钮，介绍屏幕应该淡出，但它不工作。我猜可能是在js文件中有什么错误，但我不能确定问题所在。

const game = () => {
  let pScore = 0;
  let cScore = 0;

  const startGame = () => {
    const playBtn = document.querySelector('.intro button');
    const introScreen = document.querySelector('.intro');
    const match = document.querySelector('.match');

    playBtn.addEventListener('click', () => {
      introScreen.classList('.fadeOut');

    });
  };
};

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

section {
  height: 100vh;
  background-color: rgb(39, 41, 68);
  font-family: sans-serif;
}

.score {
  color: rgb(224, 224, 224);
  height: 20vh;
  display: flex;
  justify-content: space-around;
  align-items: center;
}

.score h2 {
  font-size: 30px;
}

.score p {
  text-align: center;
  padding: 10px;
  font-size: 25px;
}

.intro {
  background-color: rgb(39, 41, 68);
  height: 50vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: space-around;
  transition: opacity 0.5s ease;
}

.intro h1 {
  font-size: 50px;
}

.intro button,
.match button {
  width: 150px;
  height: 50px;
  font-size: 20px;
  background: none;
  border: none;
  color: rgb(45, 117, 96);
  border-radius: 3px;
  background-color: rgb(45, 117, 96);
  color: rgb(224, 225, 224);
  cursor: pointer;
}

.match {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  transition: opacity 0.5s ease 0.5s;
}

.winner {
  color: rgb(224, 224, 224);
  text-align: center;
  font-size: 50px;
}

.hands,
.options {
  display: flex;
  justify-content: space-around;
  align-items: center;
}

.Player-hand {
  transform: rotatey(180deg);
}

div.fadeOut {
  opacity: 0;
  pointer-events: none;
}

div.fadeIn {
  opacity: 1;
  pointer-events: all;
}

<section>
  <div class="score">
    <div class="player-score">
      <h2>Player</h2>
      <p>0</p>
    </div>
    <div class="computer-score">
      <h2>Computer</h2>
      <p>0</p>
    </div>
  </div>
  <div class="intro">
    <h1>Rock paper scissors</h1>
    <button>Let's Play</button>
  </div>
  <div class="match fadeOut">
    <h2 class="winner">Choose an option</h2>
    <div class="hands">
      <img class="Player-hand" src="./assets/rock.png" alt="">
      <img class="computer-hand" src="./assets/rock.png" alt="">
    </div>
    <div class="options">
      <button>rock</button>
      <Button>paper</button>
      <button>scissors</button>

    </div>
  </div>
</section>