<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>文档标题</title>
</head>
<body>
<div class="main-content">
<p>.main-content{color: grey;}</p>
<h3>.main-content h3{color:green;}</h3>
<h3 class="h3">.main-content .h3{color:orange;}</h3>
<h3 id="h3">#h3{color:red;}</h3>
<h3 class="h3" id="h3" style="color: black;">style="color: black;"</h3>
</div>
<h3>h3{color:blue;}</h3>
<h3 class="h3">.h3{color:purple;}</h3>
</body>
</html>
输入 JavaScript 代码……
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.main-content{color: black;}
h3{color:blue;}
.h3{color:purple;}
.main-content h3{color:green;}
.main-content .h3{color:orange;}
#h3{color:red;}