JavaScript实现简易选项卡式年历

<!DOCTYPE html>
<html>
 <head>
 <meta charset="UTF-8">
 <title></title>
 <style type="text/css">
  #box{
  background-color: green;
  border-radius: 20px;
  padding: 10px;
  height: 800px;
  width: 450px;
  margin: 20px auto;
 
  }
  ul,li{
  margin: 0;
  padding: 0;
  list-style-type: none;
 
  }
  ul{
  overflow: hidden;
  }
  li{
  background-color: yellow;
  height: 120px;
  width:120px;
  float: left;
  margin: 10px;
  text-align: center;
  color:blueviolet;
  }
  #bottom{
  margin: 10px;
  }
  .active{
  background-color: crimson;
  }
 </style>
 </head>
 <body>
 <div id="box">
  <ul>
  <li class="active"><h2>一月</h2><p>January </p></li>
  <li><h2>二月</h2><p>February </p></li>
  <li><h2>三月</h2><p>March </p></li>
  <li><h2>四月</h2><p> April </p></li>
  <li><h2>五月</h2><p> May </p></li>
  <li><h2>六月</h2><p>June</p></li>
  <li><h2>七月</h2><p>July </p></li>
  <li><h2>八月</h2><p>August</p></li>
  <li><h2>九月</h2><p>September </p></li>
  <li><h2>十月</h2><p> October </p></li>
  <li><h2>十一月</h2><p> November </p></li>
  <li><h2>十二月</h2><p>December</p></li>
  </ul>
  <div id="bottom">
  <h2>一月</h2>
  <p>天气很好，去哪里玩呢？？？</p>
  </div>
 </div>
 <script type="text/javascript">
  var box=document.getElementById("box");
  var bottom=document.getElementById("bottom");
  var li=box.getElementsByTagName("li");
  for (var i=0;i<li.length;i++) {
  li[i].index=i;
  var arr=["一月吃牛排","二月吃意面","三月看帅哥","四月看星星"
  ,"五月吃猪蹄","六月吃西瓜","七月吃雪糕","八月吹空调","九月捡树叶","十月吃烤鸡",
  "十一月吃麻辣烫","十二月回家过年"];
  li[i].onmouseover=function(){//事件绑定
   for (var i=0;i<li.length;i++) {
   //清除所有的li的className
   li[i].className=" ";
   }
   this.className="active";//给当前的li添加className
   bottom.innerHTML='<h2>'+(this.index +1)+'月活动 </h2><p>'+arr[this.index]+'</p>';
  }
 
  }
 </script>
 </body>
</html>