Shadow DOM，然后遇到了一个问题。:root {}语法来声明一些CSS variables. 但不幸的是，它不起作用。在1.html
<!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>Shadow DOM</title>
</head>
<body>
<square-element></square-element>
<script src="./1.js"></script>
</body>
在1.js：
const htmlCode = `
<!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>HTML Shadow DOM</title>
<style>
* {
box-sizing: border-box;
margin: 0;
padding: 24px;
}
:root {
--bg-color: …