title: Remove the top margin of header in bootstrap
body: <p>HTML</p>
  
  <pre><code>&lt;div class="container-fluid"&gt;
    &lt;div class="row"&gt;
      &lt;div class="page-header header_site"&gt;
        &lt;h1&gt;&lt;font&gt;ABC Company&lt;/font&gt;&lt;/h1&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>CSS Code: </p>
  
  <pre><code>.header_site {
    background-color: darkblue;
  }
  
  font {
    color: white;
    margin: auto 160px auto 160px;
  }
  </code></pre>
  
  <p>I want to remove the top-margin as marked in the following figure.</p>
  
  <p><a href="https://i.stack.imgur.com/9pkNe.png" rel="noreferrer"><img src="https://i.stack.imgur.com/9pkNe.png" alt="enter image description here"></a> </p>