第一个练习（一）
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.box{
width: 600px;
margin: 0 auto;
}
.top{
width: 500px;
height: 120px;
background-color: #36c3fd;
}
.bottom{
width: 496px;
height: 498px;
border: 2px solid #128fc2;
border-top: transparent;
}
.item{
width: 496px;
height: 100px;
border-bottom:2px solid #ecf4fa;
}
</style>
</head>
<body>
<div class="box">
<div class="top"></div>
<div class="bottom">
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
</div>
</div>
</body>
</html>
