Create custom HTML5 tag
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Customer html5 tag</title>
<script>
customElements.define('x-foo')
</script>
<style>
x-foo {
color: red;
font-size: 10rem;
}
</style>
</head>
<body>
<x-foo>
custom html5 tag
</x-foo>
</body>
</html>