在< style > 标签中
p {}: 所有p标签; p.ad{}: p 标签中 class 为ad的; p#aa{}: p标签中id为aa的;
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1">
<title>元素选择符</title>
<meta name="Keywords" content="关键字">
<meta name="description" content="简介">
<!-- 元素选择符 -->
<style>
/*所有P标签*/
p {
color: #027e02;
}
/*p标签中 class为ab的*/
p.ab {
color: darkseagreen;
}
/*p标签中 id为aa的*/
p#aa {
background-color: #10f574;
}
</style>
</head>
<body>
<p id="aa">Lorem ipsum dolor.</p>
<p>Accusantium, architecto, illo.</p>
<p class="ab">Assumenda, molestiae rerum.</p>
<span class="ab">Lorem ipsum dolor.</span>
</body>
</html>