title: Bootstrap 4 navbar-inverse doesn't have colour
body: <p>Recently I decided to try new bootstrap version (4). I did everything right with files (my html below)</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html lang="pl"&gt;
  &lt;head&gt;
      &lt;meta charset="UTF-8"&gt;
      &lt;meta name="viewport" content="width=device-width, initial-scale=1.0"&gt;
      &lt;meta http-equiv="X-UA-Compatible" content="ie=edge"&gt;
      &lt;title&gt;Bootstrap 4 website&lt;/title&gt;
      &lt;link rel="stylesheet" href="css/bootstrap.min.css"&gt;
      &lt;link rel="stylesheet" href="css/style.css"&gt;
  &lt;/head&gt;
  &lt;body&gt;
  
      &lt;nav class="navbar navbar-inverse"&gt;
          &lt;a href="#"&gt;Link1&lt;/a&gt;
      &lt;/nav&gt;
  
      &lt;!-- JS scripts here --&gt;
      &lt;script src="js/jquery-3.2.1.min.js"&gt;&lt;/script&gt;
      &lt;script src="js/popper.min.js"&gt;&lt;/script&gt;
      &lt;script src="js/bootstrap.min.js"&gt;&lt;/script&gt;
      &lt;script src="js/script.js"&gt;&lt;/script&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>but my navbar (navbar-inverse) has no colour. Have You ever seen something similar with Bootstrap 4? </p>