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<!DOCTYPE HTML>
<html lang="zh-cn">
<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>布局练习</title>
<style>
    html,body,header,main,footer{
        padding: 0;
        margin: 0;
    }

    html,body{
        height: 100%;        
    }

    body{
        display: flex;
        flex-direction: column;
    }

    header{
        flex: 0 0 60px;
        background-color:#111;
    }
    
    footer{
        flex: 0 0 40px;
        background-color:#222;
    }

    main{
        flex: 1;
        display: flex;

    }

    nav,aside{
        flex: 0 0 150px;
    }

    section{
        flex: 1;
        background-color: #ccc;
        display: flex;
        justify-content: center;
        align-items: center;
    } 

    .box{
        width: 100px;
        height: 100px;
        background-color: red;
    }
</style>
</head>
<body>
<header></header>
<main>
    <nav></nav>
    <section>
        <div class="box"></div>
    </section>
    <aside></aside>
</main>
<footer></footer>
</body>
</html>