<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<h2>横向伸缩：</h2>
<div class="flex">
<div class="left"></div>
<div class="cent"></div>
<div class="right"></div>
</div>
<style>
.flex{ display: flex; height: 100px; border:1px solid #ccc;}
.flex div{ 50px; height: 100px; border:1px solid #eee;}
.flex .left{ flex:1;}
.flex .cent{ flex:5;}
.flex .right{ flex:1;}
</style>
<h2>纵向伸缩：</h2>
<div class="v_flex">
<div class="top"></div>
<div class="mid"></div>
<div class="bot"></div>
</div>
<style>
.v_flex{ display: flex; flex-direction:column; height: 300px; margin-top:20px; border: 1px solid #ccc;}
.v_flex div{ height: 50px; border:1px solid #eee;}
.v_flex .mid{ flex: 1;}
</style>
</body>
</html>