Background image in Polymer component example

tester-app.html

<link rel="import" href="../../bower_components/polymer/polymer.html">

<dom-module id="tester-app">
  <template>
    <style>
      :host {
        display: block;
      }
      img.bg {

        /* Stick it to the upper left hand corner */
        position: fixed;
        top: 0;
        left: 0;

        /* Make it stretch to any screen size */
        width: 100%;
        height: auto;
        min-height: 100%;

        /* set min-width to image width to maintain scale */
        min-width: 1024px;

        /* Make the deepest layer */
        z-index: -999;
      }
        @media screen and (max-width: 1024px) { /* recenter the image on smaller screens */
          img.bg {
            left: 50%;
            margin-left: -512px;   /* 50% */
          }
        }

    </style>
    <img class="bg" src="../images/seigaiha.png" alt="">
    <h1>Test</h1>
  </template>

  <script>
    Polymer({

      is: 'tester-app',

      properties: {
        prop1: {
          type: String,
          value: 'tester-app',
        },
      },

    });
  </script>
</dom-module>