title: How to remove the square border from around a button which has already been visited?
body: <p>After I click one of the buttons and go back to the main page, the button that I clicked is bordered with a square blue border. How can I remove this border so that there's no square border around the circle button after I have clicked it?</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>button {
    width: 100px;
    height: 100px;
    background: #3F6;
    border-color: #000;
    border-radius: 4em;
  }
  button:hover {
    background: #F00;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;a href="#" target="_blank"&gt;&lt;button&gt;Test&lt;/button&gt;&lt;/a&gt;
  &lt;a href="#" target="_blank"&gt;&lt;button&gt;Test&lt;/button&gt;&lt;/a&gt;
  &lt;a href="#" target="_blank"&gt;&lt;button&gt;Test&lt;/button&gt;&lt;/a&gt;
  &lt;a href="#" target="_blank"&gt;&lt;button&gt;Test&lt;/button&gt;&lt;/a&gt;</code></pre>
  </div>
  </div>
  </p>