                        课程
                    
                        /前端开发
                        
                            /JavaScript
                        
                        /JavaScript入门篇

可以参考下

<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>className属性</title>
<style>
    body{ font-size:16px;}
    .one{
       border:1px solid #eee;
       width:230px;
       height:50px;
       background:#ccc;
       color:red;
    }
   .two{
       border:1px solid #ccc;
       width:230px;
       height:50px;
       background:#9CF;
       color:blue;
   }
   </style>
</head>
<body>
    <p id="p1" > JavaScript使网页显示动态效果并实现与用户交互功能。</p>
    <input type="button" value="添加样式1" onclick="add()"/>
    <input type="button" value="添加样式2" onclick="acc()"/>
   <p id="p2" class="one">JavaScript使网页显示动态效果并实现与用户交互功能。</p>
    <input type="button" value="更改外观1" onclick="modify()"/>
    <input type="button" value="更改外观2" onclick="modifa()"/>

   <script type="text/javascript">
       function add(){
          var p1 = document.getElementById("p1");
          p1.className="one";

       }
       function acc(){
          var p1 = document.getElementById("p1");
          p1.className="two";

       }
       function modify(){
          var p2 = document.getElementById("p2");
          p2.className="two";
       }
       function modifa(){
          var p2 = document.getElementById("p2");
          p2.className="one";
       }
   </script>
</body>
</html>