<!DOCTYPE>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>固定的底栏</title>
<style>
.rongqi{ display:flex; flex-direction:column; min-height:100vh;}
.shang{ background-color:#66CCCC; height:60px;}
.zhong{ background-color:#CCC; flex:1;}
.xia{ background-color: #09F; height:60px;}
</style>
</head>
<body class="rongqi">
<div class="shang">
01
</div>
<div class="zhong">
02
</div>
<div class="xia">
03
</div>
</body>
</html>