实现布局中间自适应宽度，左右两栏固定宽度
<style>
.box{
display:flex;
}
.left{
width: 200px;
height: 600px;
background:red;
}
.right{
width: 200px;
height: 600px;
background:red;
}
.center{
width: 100%;
height:600px;
background:green;
}
</style>
</head>
<body>
<div class="box" >
<div class="left"></div>
<div class="center"></div>
<div class="right"></div>
</div>