<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Common selectors in css</title>
<style type="text/css">
/*Element selector*/
/**{color: red;}*/
p{text-align: center;}
## /*Category selector*/
.c1{color: red; }
/*ID selector*/
/*#one{color: blue; font-size: 60px;}*/
/*Priority id>color>mark*/
</style>
</head>
<body class="box">
<p>php</p>
<span classs=" c1">Hello! 123</span>
<p>I am 321</p>
</body>
</html>
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
You wrote it wrong, calss. . .
is class