Place a full size image in the background of the website. Demo
Put the <img-background> web component on your website and include img-background.html, for example, after opening <body> tag:
<body>
<img-background src="path-to-your-image"></img-background>
<link rel="import" href="./dist/img-background.html">
<!--- rest of site --->
</body>
Put the <img-background> web component on your website and include img-background-polymer.html, for example, after opening <body> tag:
<body>
<img-background src="path-to-your-image"></img-background>
<link rel="import" href="../dist/img-background.html">
<!--- rest of site --->
<script src="//cdnjs.cloudflare.com/ajax/libs/polymer/0.2.3/platform.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/polymer/0.2.3/polymer.js"></script>
<link rel="import" href="./dist/polymer-project/img-background.html">
</body>