Defining an element with no content.
<dom-module id="empty-element">
<template>
<style>
</style>
</template>
<script>
Polymer({
is: 'empty-element',
});
</script>
</dom-module>
And then you can use the new element in any other pages.
<!DOCTYPE html>
<html>
<head>
<!-- Using lite version as Polymer does not require Polyfill for Shadow Dom -->
<script src="path/to/bower_components/webcomponentsjs/webcomponents-lite.min.js"></script>
<!-- Importing the element assuming file name is also empty-element.html -->
<link rel="import" href="empty-element.html">
</head>
<body>
<empty-element></empty-element>
</body>
</html>