css3 盒子四角边框的实现_css3 box四个角-优快云博客

本文链接：https://blog.youkuaiyun.com/IT_iosers/article/details/112202519

重点1、:父相子绝 2、通过伪类before after 添加相应方向的边框

在这里插入图片描述
实例代码:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        html,body{
            width: 100%;
            height: 100%;
            display: flex;
            justify-content: center;
            align-items: center;

        }
        .box{
            width: 200px;
            height: 200px;
            background-color: black;
            /* 要边框的盒子 相对地址 */
            position: relative;
        }
        /* 通过before after 两个伪类制作 上方的装饰*/
        .box::before{
            content: '';
            position: absolute;
            left: 0;
            top: 0;
            border-left: 2px solid green;
            border-top: 2px solid green;
            width: 10px;
            height: 10px;
        }
        .box::after{
            content: '';
            position: absolute;
            right: 0;
            top: 0;
            border-right: 2px solid green;
            border-top: 2px solid green;
            width: 10px;
            height: 10px;
        }
        .boxItem{
            position: absolute;
            bottom: 0px;
            width: 100%;
            /* border: 1px solid red; */
        }
        .boxItem::before{
            content: '';
            position: absolute;
            left: 0;
            bottom: 0;
            border-left: 2px solid green;
            border-bottom: 2px solid green;
            width: 10px;
            height: 10px;
        }
        .boxItem::after{
            content: '';
            position: absolute;
            right: 0;
            bottom: 0;
            border-right: 2px solid green;
            border-bottom: 2px solid green;
            width: 10px;
            height: 10px;
        }
        
    </style>
</head>
<body>
    <div class="box">
        <div class="boxItem"></div>
    </div>
</body>
</html>