t>
    </polymer-element>

    <my-css-transition id="my-transition-top" transitionType="top"></my-css-transition>
    <my-css-transition id="my-transition-bottom" transitionType="bottom"></my-css-transition>

my-css-transition-demo.html

    <link href="components/core-meta/core-meta.html" rel="import">
    <link href="my-css-transition.html">

    <div id="animate-me"></div>

    <script src="core-transition-css-1.js"></script>

The first element in the template of a `<core-transition-css>` object should 