title: Border color for input in Bootstrap
body: <p>I want to achieve such an effect as here <a href="https://zapodaj.net/c0e251a5b8ff2.png.html" rel="nofollow noreferrer">https://zapodaj.net/c0e251a5b8ff2.png.html</a> My current code looks like this
  <a href="https://codepen.io/anon/pen/RQWvwJ" rel="nofollow noreferrer">https://codepen.io/anon/pen/RQWvwJ</a> So I'm trying for input</p>
  
  <pre><code>&lt;div class="form-group has-warning" id="form-username"&gt;
     &lt;label class="control-label" for="username"&gt;Your username&lt;/label&gt;
     &lt;input name="username" id="username" type="text" maxlength="36" class="form-control" /&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>add a class <code>has-warning</code> to change the color, but it does not. I'm using Bootstrap 4.0.0.</p>
  
  <p>How do you set a border for the input field?</p>