css 实现三栏布局的四种方式

三栏布局就是左中右，左右两边固定，中间自适应。

1. 绝对定位

    <div class="left">左边</div>
    <div class="middle">中间</div>
    <div class="right">右边</div>

        body {
            padding: ;
            margin: ;
        }

        /* 绝对定位 */
        .left, .right {
            position: absolute;
            top: ;
        }
        .left {
            background: red;
            width: 200px;
            left: ;
        }
        .middle {
            background: blue;
            margin:  200px;
        }
        .right {
            background: green;
            width: 200px;
            right: ;
        }

2. flex

    <div class="left">左边</div>
    <div class="middle">中间</div>
    <div class="right">右边</div>

        body {
            display: flex;
            padding: ;
            margin: ;
        }
        .left {
            background: blue;
            flex: 200px  ;
        }
        .middle {
            background: red;
            flex: ;
        }
        .right {
            background: green;
            flex:   200px;
        }

3. 双飞翼

    <div class="middle">
        <div class="inner">
            中间
        </div>
    </div>
    <div class="left">左边</div>
    <div class="right">右边</div>

        body {
            padding: ;
            margin: ;
        }
        .left, .middle, .right {
            float: left;
        }
        .left {
            background: red;
            width: 200px;
            margin-left: -%; /* 使left移到middle的左边 */
        }
        .right {
            background: red;
            width: 200px;
            margin-left: -200px; /* 使right移到middle的右边 */
        }
        .middle {
            background: blue;
            width: %;
        }
        .inner {
            margin:  200px;
        }

4. 浮动

    <div class="left">左边</div>
    <div class="right">右边</div>
    <div class="middle">中间</div>

        .left {
            float: left;
            background: blue;
            width: 200px;
        }
        .middle {
            margin:  200px;
            background: red;
            width: %;
        }
        .right {
            float: right;
            background: green;
            width: 200px;
        }

参考：https://segmentfault.com/a/1190000007729716