6.2 浮动元素对兄弟元素影响div:last-child{ background-color: blue; /* 清除

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<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width: 100px;
            height: 100px;
            background-color: red;

        }
        div:first-child{
            float: left;
        }
        div:last-child{
            background-color: blue;
            /* 清除浮动元素对兄弟元素影响 */
            clear: both;
        }
    </style>
</head>
<body>
    <div></div>
    <div></div>
</body>
</html>