header.component.html

<nav class="navbar navbar-expand-md navbar-dark bg-dark mb-4">
  <a class="navbar-brand" href="#">DotNetGigs</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarCollapse" aria-controls="navbarCollapse" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
      <div class="collapse navbar-collapse" id="navbarCollapse">
        <ul class="navbar-nav mr-auto">
          <li class="nav-item active">
            <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
          </li>
          <li class="nav-item">
            <a class="nav-link" href="#">Link</a>
          </li>
          <li class="nav-item">
            <a class="nav-link disabled" href="#">Disabled</a>
          </li>
        </ul>      
      </div>
    </nav>