title: Polymer.js Paper Tabs styling
body: <p>I'm wondering how to implement a yellow, sliding <code>border-bottom</code> property as seen on example <strong>C.</strong> "The bar slides to the selected tab"<br>
  <a href="https://www.polymer-project.org/0.5/components/paper-tabs/demo.html" rel="nofollow">https://www.polymer-project.org/0.5/components/paper-tabs/demo.html</a> .</p>
  
  <p>Inspecting the CSS, I didn't see a <code>border-bottom</code> property.</p>
  
  <p>Has someone tried to recreate it or there any good resources on that?</p>