<!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;
}
div {
width: 100px;
height: 100px;
background-color: yellow;
}
div::before {
content: '123';
}
</style>
</head>
<body>
<div></div>
</body>
</html>
我想给div的元素前添加一些内容为什么会在两个地方出现添加的内容呢？
