{"html":"<!DOCTYPE html>\n<html>\n\n<head>\n    <meta charset=\"UTF-8\">\n    <style>\n       /* 填写样式 */\n       div::after{\n        content:'';\n        display:block;\n\n        width:20px;\n        height:20px;\n        background-color:rgb(255,0,0);\n       }\n    </style>\n</head>\n\n<body>\n  <div></div> \n    <script type=\"text/javascript\">\n        /* 填写JavaScript */\n        \n    </script>\n</body>\n\n</html>","css":"","js":""}

伪元素默认是行内元素,设置宽高无效,所以要用display:block;

前伪元素和后伪元素都必须要加content：“”；如果要写文本的话就是吧文本写在引号内