demo.html：
<!DOCTYPE html>
<html >
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
span {
border: 1px solid #000;
}
span::before {
content: attr(data-text); /* 伪元素通过attr()获取标签自定义属性的值 */
}
</style>
</head>
<body>
<span data-text="aaa">bbb</span> <!-- data-text标签自定义的属性 -->
</body>
</html>
![用 Canvas 编织璀璨星空图[图]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)