Pseudo-elements are inline elements by default

Notes on the use of pseudo-elements:
The common pseudo-elements are after and before. When using, you must add the content attribute
before to add the first child element
to this element; aftere add the last child element to this element.
The default is inline (line-level element), if you want to set the size of it, it is generally set to block or set to float or flex.
insert image description here
Pseudo-element and floating use:
use two pictures to achieve a double door effect, a background picture, and a moving picture:

Background image:
insert image description here
moving image:

hover effect:

The picture moves to both sides (one left and one right)
insert image description here
layout idea: use the parent as the background and float it from the level!

<!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>
        * {
    
    
            margin: 0;
            padding: 0;
        }
        
        .box {
    
    
            width: 1366px;
            height: 600px;
            margin: 0 auto;
            background: url('./images/bg.jpg');// 背景图
            overflow: hidden;
        }
        
        // 伪元素的公共样式
        .box::before,
        .box::after {
    
    
            /* 行内标签，宽高看不见，需要使用float或者display */
            float: left;
            content: '';
            /* 只需要显示一半 */
            width: 50%;
            height: 600px;
            background-image: url(./images/fm.jpg);// 移动的图
            transition: all .5s;
        }
        
        /* 移动一下图片的位置，bck-position除了写像素值，还可以写right这样的方向值，直接定位到最右侧 */
        /* right为0表示从右侧开始显示。而且只是一半，所以是右半部分 */
        .box::after {
    
    
            background-position: right 0;//设置背景图的位置，达到只要右半部分的效果
        }

        /* 鼠标移入的时候的位置改变的效果 */
        /* 移入之后看不见自己，则至少是自身的宽度，即100% */
        .box:hover::before {
    
    
            /* 注：这里的100%是自身的宽度 */
            transform: translate(-100%);
        }

        .box:hover::after {
    
    
            transform: translateX(100%);
        }
    </style>
</head>

<body>
    <div class="box">

    </div>
</body>

</html>
注：代码和素材均来自B站黑马的网课

Pseudo-elements are inline elements by default

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