CSS布局（圣杯布局、双飞翼布局、水平垂直居中）

一、圣杯布局

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要求：三列布局；中间主体内容前置，且宽度自适应；两边内容定宽
好处：重要的内容放在文档流前面可以优先渲染
原理：利用相对定位、浮动、负边距布局，而不添加额外标签

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        body {
            min-width: 600px;
        }

        header, footer {
            width: 100%;
            height: 50px;
            line-height: 50px;
            background: papayawhip;
            text-align: center;
        }
        .box {
            padding: 0 200px;
        }
        .clearfix::after {
            content: '';
            display: block;
            clear: both;
        }
        .main {
            float: left;
            background: pink;
            width: 100%;
            height: 300px;
        }
        .left {
            float: left;
            width: 200px;
            height: 300px;
            background: skyblue;
            margin-left: -100%;
            position: relative;
            left: -200px;
        }
        .right {
            float: left;
            width: 200px;
            height: 300px;
            background: yellow;
            margin-left: -200px;
            position: relative;
            right: -200px;
        }
    </style>
</head>
<body>
<header>圣杯布局</header>
<div class="box clearfix">
    <div class="main text">
        main
    </div>
    <div class="left text">
        left
    </div>
    <div class="right text">
        right
    </div>
</div>
<footer>footer</footer>
<script>
</script>

</body>
</html>

二、双飞翼布局

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双飞翼布局：对圣杯布局（使用相对定位，对以后布局有局限性）的改进，消除相对定位布局
原理：主体元素上设置左右边距，预留两翼位置。左右两栏使用浮动和负边距归位，消除相对定位。

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        body {
            min-width: 600px;
        }

        header, footer {
            width: 100%;
            height: 50px;
            line-height: 50px;
            background: papayawhip;
            text-align: center;
        }

        .box {
        }

        .clearfix::after {
            content: '';
            display: block;
            clear: both;
        }

        .main {
            float: left;
            background: pink;
            width: 100%;
            height: 300px;
        }

        .main-content {
            margin-left: 200px;
            margin-right: 200px;
            height: 100%;
        }

        .left {
            float: left;
            width: 200px;
            height: 300px;
            background: skyblue;
            margin-left: -100%;
        }

        .right {
            float: left;
            width: 200px;
            height: 300px;
            background: yellow;
            margin-left: -200px;
        }
    </style>
</head>
<body>
<header>双飞翼布局</header>
<div class="box clearfix">
    <div class="main text">
        <div class="main-content">
            main
        </div>
    </div>
    <div class="left text">
        left
    </div>
    <div class="right text">
        right
    </div>
</div>
<footer>footer</footer>
</body>
</html>