代码编辑器：
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1
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<meta charset="utf-8">3
<link href="/static/next/css/tryit.css?v=2017082407" rel="stylesheet"/>4
<script src="https://cdn.staticfile.org/jquery/2.2.4/jquery.min.js"></script>5
<script>6
$(document).ready(function(){7
$("button").click(function(){8
$("p:first").addClass("intro note");9
});10
});11
</script>12
<style>13
.intro{14
font-size:30px;15
color:blue;16
}17
.note{18
background-color:yellow;