HTML 练习清除浮动 :after

为 clearfix 类所在的 div 内部最后处添加一个 div 标签，内容为 . ，高度为0，隐藏

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .left{
            float: left;
        }
        .container{
            background-color: red;
        }

        .container .item{
             180px;
            height: 150px;
            background-color: #303a40;
            border: 1px solid red;
        }
        .clearfix:after{
            content: '.';
            display: block;
            clear: both;
            visibility: hidden;
            height: 0;
        }
    </style>
</head>
<body>
    <div class="container clearfix">
        <div class="item left"></div>
        <div class="item left"></div>
        <div class="item left"></div>
        <div class="item left"></div>
        <div class="item left"></div>
        <div class="item left"></div>
        <div class="item left"></div>
        <div class="item left"></div>

    </div>
    <div>abcd</div>
</body>
</html>