title: remove border that appears when clicking button
body: <p>I have a rating form in which when I click on a star, the following border appears:</p>
  
  <p><a href="https://i.stack.imgur.com/tYilN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/tYilN.png" alt="rating-form"></a></p>
  
  <p>implement the following example: <a href="https://stackblitz.com/edit/angular-material-star-rating?file=app%2Fstar-rating%2Fstar-rating.component.ts" rel="nofollow noreferrer">angular-material-star-rating</a></p>
  
  <p>How can I remove this border?</p>