title: Remove dotted line around clicked button
body: <p>I have a div that, when clicked, the button inside of it will create an outline around it, like so: </p>
  
  <p><a href="https://i.stack.imgur.com/pEr53.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pEr53.png" alt="image outline"></a></p>
  
  <p>**Code: ** </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.slide-arrow {
    color: #fff;
    background-color: #9E9997;
    border: none;
    padding: 16px 10px 17px 10px;
    font-size: 25px;
    opacity: 0.5;
    outline: 0;
  }
  
  .slide-arrow-right {
    position: absolute;
    top: 50%;
    right: 0%;
    transform: translate(0%, -50%);
    -ms-transform: translate(0%, -50%);
    margin-right: -1px;
    border-bottom-left-radius: 4px;
    border-top-left-radius: 4px;
  }
  
  .slide-arrow-left {
    position: absolute;
    top: 50%;
    left: 0%;
    transform: translate(0%, -50%);
    -ms-transform: translate(-0%, -50%);
    border-bottom-right-radius: 4px;
    border-top-right-radius: 4px;
  }
  
  .slide-arrow:hover {
    opacity: 0.7;
  }
  
  .slide-arrow:active {
    background-color: #D47C7C;
  }
  
  .slide-arrow i {
    font-size: 32px;
    outline: 0 !important;
  }
  
  .slide-arrow i:focus {
    outline: 0 !important;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;button class="slide-arrow slide-arrow-right" onclick="plusDivs(1)"&gt;&lt;i class="fa fa-angle-double-right"&gt;&lt;/i&gt;&lt;/button&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>I want this removed. But when applying <code>outline: 0 !important;</code> to just about everything, nothing seems to work. This only seems to happen in firefox.</p>