provides a scroller -->
  <app-header-layout has-scrolling-region>
    <app-header slot="header" effects="waterfall" condenses reveals>
      <app-toolbar>
        <paper-icon-button icon="menu"></paper-icon-button>
        <div main-title></div>
        <paper-icon-button icon="search"></paper-icon-button>
      </app-toolbar>
      <app-toolbar></app-toolbar>
      <app-toolbar>
        <div spacer main-title>My Drive</div>
      </app-toolbar>
    </app-header>

    <sample-content size="100"></sample-co