title: How can we slow down the opening of mat-expansion panel using angular-animations and give them a fade in out effect
body: <p>How can I animate mat-expansion panel on open and close.</p>
  
  <pre><code>trigger('fadeInOut', [
        state('open', style({
          opacity:1
        })),
        state('closed', style({
          opacity:0
        })),
        transition('open=&gt;closed', animate('1.5s ease-out')),
        transition('closed=&gt;open', animate('1.5s ease-out'))
  ]),
  </code></pre>