test.html

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

<polymer-element name="my-marquee" noscript>
  <template>
    <style>
    div {
      position: absolute;
      -webkit-animation: background-animation 3s ease 0s infinite alternate;
    }
    @-webkit-keyframes background-animation {
      0% {
        left: 0;
      }
      100% {
        left: 200px;
      }
    }
    </style>
    <div class="test"><content></content></div>
  </template>
</polymer-element>

<my-marquee>test</my-marquee>