例
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<style>
p{
color: blue;
}
.green{
color: green;
}
.red{
color: #FF0000;
}
#darkgold{
color: darkgoldenrod;
font-size: 36px;
}
span{
color: pink ;
}
</style>
</head>
<body>
<p>段落1</p>
<p class="green">段落2</p>
<p class="red" >段落3</p>
<h1>标题1</h1>
<h1>标题2</h1>
<!-- id选择器与class选择器比较 -->
<h1 id="darkgold" class="red" >标题3</h1>
<!-- class选择器与标签比较 -->
<span class="red" >span行元素</span>
<!-- id优先级>class类>标签选择器 -->
</body>
</html>