6.3 浮动元素对父元素的影响清除浮动元素对其他元素影响 */ /* 2.在浮动元素和非浮动元素间添加一个空块级元素 *

<!DOCTYPE html>
<html lang="en">
<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>
        .parent{
            border: 10px solid red;
            margin-top: 10px;
        }
        .child{
            width: 100px;
            height: 100px;
            background-color: blue;
            float: left;
        }
        /* 清除浮动元素对其他元素影响 */
        /* 2.在浮动元素和非浮动元素间添加一个空块级元素 */
        .clear{
            clear: both;
        }
        /* 3.消除浮动元素对父元素的影响 使用伪元素 */
        .parent:nth-child(2)::after{
            content: "";
            display: block;
            clear: both;
        }
    </style>
</head>
<body>
    <div class="parent">hello css</div>
    <div class="parent">
        <div class="child">1</div>
        <div class="child">2</div>
        <div class="child">3</div>
        <div class="child">4</div>
    </div>
    <div class="clear"></div>
    <div class="parent">hello css</div>
</body>
</html>