##<paper-button>
Material design: Buttons
paper-button is a button. When the user touches the button, a ripple effect emanates
from the point of contact. It may be flat or raised. A raised button is styled with a
shadow.
Example:
<paper-button class="pink">link</paper-button>
<paper-button raised class="indigo">raised</paper-button>
<paper-button toggles raised class="green">toggles</paper-button>
<paper-button disabled class="disabled">disabled</paper-button>