Example with style
Start
<head>
<style amp-custom>
h1 { color:red; }
</style>
</head>
<body>
<h1>Red Headline</h1>
</body>
End
Start
<head>
<style amp-custom>
h1 { color:red; }
</style>
</head>
<body>
<h1>Red Headline</h1>
</body>
End