CSS：
* { padding:0; margin:0;}body { font-size:12px; font-family:"微软雅黑";}form { width:500px; position:absolute; top:50%; left:50%; margin:-70px 0 0 -250px;}fieldset { border:2px solid rgb(4, 122, 201); padding:10px;}legend { font-size:13px; font-weight:bold; padding:10px; color:rgb(4, 122, 201);}div { padding:5px 0;}label { color:rgb(4, 122, 201);}input { height:25px; border:1px solid #C9C9C9; width:200px; font-size:12px; font-family:"微软雅黑"; padding:0 5px; line-height:25px;}textarea { width:200px; height:100px; border:1px solid rgb(4, 122, 201); font-size:12px; font-family:"微软雅黑"; padding:5px; vertical-align:middle;}.focusa { border:1px solid rgb(4, 122, 201); background:#FFF0FF;}Html
<html ><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><link rel="stylesheet" type="text/css" href="css/demo13.css"/><script src="js/jquery-3.4.1.min.js"></script><script type="text/javascript">$(document).ready(function(){ $(":input").focus(function(){ $(this).addClass("focusa"); if ($(this).val()==this.defaultValue){ $(this).val(""); } }).blur(function(){ $(this).removeClass("focusa"); if ($(this).val()==""){ $(this).val(this.defaultValue); } });});</script></head><body> <form action="" method="post"> <fieldset> <legend>个人信息</legend> <div> <label for="username">姓名：</label> <input type="text" id="username" value="请输入姓名" /> </div> <div> <label for="pass">密码：</label> <input type="password" id="pass" value="请输入密码" /> </div> <div> <label for="content">内容：</label> <textarea id="content">内容</textarea> </div> </fieldset> </form></body></html>
