title: Why my navbar-dark bg-dark classes won't work on bootstrap 4
body: <p>i'm new to bootstrap.I tried adding navigation bar to html page using bootstrap classes but .navbar-dark .bg-dark or .navbar-light .bg-light tags aren't working.</p>
  
  <p>Here's my code</p>
  
  <p>''''</p>
  
  <pre><code>&lt;body&gt;
      &lt;div class="container-fluid"&gt;
      &lt;nav class="navbar  navbar-expand-md navbar-dark bg-dark"&gt;
          &lt;ul class="nav navbar-nav"&gt;
              &lt;li class="nav-item"&gt;
                  &lt;a class="nav-link" href="#"&gt;Link1&lt;/a&gt;
              &lt;/li&gt;
              &lt;li class="nav-item"&gt;
                  &lt;a class="nav-link" href="#"&gt;Link1&lt;/a&gt;
              &lt;/li&gt;
              &lt;li class="nav-item"&gt;
                  &lt;a class="nav-link" href="#"&gt;Link1&lt;/a&gt;
              &lt;/li&gt;
              &lt;li class="nav-item"&gt;
                  &lt;a class="nav-link" href="#"&gt;Link1&lt;/a&gt;
              &lt;/li&gt;
          &lt;/ul&gt;
      &lt;/nav&gt;
  &lt;/div&gt; 
  </code></pre>
  
  <p>''''</p>