初学求教大神!谢谢!!谁能把这个交互页面 js 代码写给我
如图所示:登录列表框没有获得点击时,提示内容在列表框内显示灰色,当鼠标点击列表框时,提示内容颜色改变自动滑动到列表框边框里面。哪位大神能把这个js简洁明了的写给我,谢谢了!求大神赐教!!!跪谢大神!

<html> <head> <!--<script type="text/javascript" src="http://code.--> <script type="text/javascript" src="jquery-1.11.0.min.js"></script> <script type="text/javascript"> $(function(){ $("input").focus(function(){ $("span, div").addClass("focus"); }).blur(function(){ $("span, div").removeClass("focus"); }); }); </script> <style type="text/css"> *{padding: 0; margin: 0; font-size: 14px; font-family: "宋体";} span{ position: absolute; z-index: -1; left: 8px; color: gray; } span.focus{ top: -10px; color: purple; z-index: 2; background: white; } input{ height: 16px; line-height: 14px; border: none; position: absolute; width: 200px; left: 5px; background: transparent; } .out-side{ margin: 20px; height: 16px; position: relative; border: 1px gray solid; float: left; border-radius: 4px; padding: 5px; width: 200px; } .out-side.focus{ border-color: purple; } </style> </head> <body> <div> <div class="out-side"> <span>用户名/邮件</span> <input type="text" name="usr" class="usr"/> </div> </div> </body> </html>