纯 JS 实现 Toast 提示框：HTML、CSS 和 JavaScript 代码

<div id='toast'></div>
<style>
#toast {
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background-color: #000;
  color: #fff;
  padding: 10px 20px;
  border-radius: 5px;
  z-index: 9999;
  opacity: 0;
  transition: opacity 0.3s ease-in-out;
}

#toast.show {
  opacity: 1;
}
</style>
<script>
function showToast(message, duration) {
  var toast = document.getElementById('toast');
  toast.innerHTML = message;
  toast.classList.add('show');
  setTimeout(function() {
    toast.classList.remove('show');
  }, duration);
}

// 示例，显示 'Hello World' 3秒钟
showToast('Hello World', 3000);
</script>