title: ion-segment-button indicator outline border
body: <p>I'm using Ionic/Angular v5 and I'm trying to style an ion-segment set of buttons so as to have an OUTLINE border as an indicator
  I tried using the shadow parts &quot;indicator&quot; and &quot;indicator-background&quot; in order to set the color and thickness of the border, and the background color to be transparent so as to show as an &quot;outline&quot;, but it does not get the settings</p>
  <p>I am getting
  <a href="https://i.stack.imgur.com/YwCvX.png" rel="nofollow noreferrer">this</a> but what I am trying to achieve is have a red border AROUND the checked button and still show the &quot;original&quot; background color of the button.</p>
  <p>My CSS is:</p>
  <pre><code>&amp;::part(indicator) {
    height: 100%;
    color: var(--ion-color-tertiary);
    border-width: 3px;
    border-color: var(--ion-color-tertiary);
  }
  &amp;::part(indicator-background) {
    color: transparent;
  }
  </code></pre>
  <p>Any ideas on how to achieve the style I'm looking for ?</p>
  <p>Many thanks
  Chris</p>