html 类和id
DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>title>
<style type="text/css">
.cla1{
background-color: blue;
color: red;
}
span.red{
color: green;
}
#sec{
color: black;
text-align: center;
}
style>
head>
<body>
<div class="cla1">
<h1>this is div_h1h1>
<p>text textp>
div>
<h1>My <span class="red">Importantspan> Heading
h1>
<h1 id="sec">SecondH1h1>
body>
html>