效果图：(红色方块可任意拖动)
代码如下：
<meta charset=UTF-8>
<meta name=Generator content=EditPlus:registered:>
<meta name=Author content=>
<meta name=Keywords content=>
<meta name=Description content=>
<title>Document</title>
<style type=text/css>
*{
margin:0;
padding:0;
}
body{
background:ur
