<header class="site-header">
  <nav class="navbar navbar-expand-md navbar-dark bg-steel fixed-top">
    <div class="container">
      <a class="navbar-brand mr-4" href="/">Flask Blog</a>
      <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarToggle" aria-controls="navbarToggle" aria-expanded="false" aria-label="Toggle navigation">
        <span class="navbar-toggler-icon"></span>
      </button>
      <div class="collapse navbar-collapse" id="navbarToggle">
        <div class="navbar-nav mr-auto">
          <a class="nav-item nav-link" href="/">Home</a>
          <a class="nav-item nav-link" href="/about">About</a>
        </div>
        <!-- Navbar Right Side -->
        <div class="navbar-nav">
          <a class="nav-item nav-link" href="/login">Login</a>
          <a class="nav-item nav-link" href="/register">Register</a>
        </div>
      </div>
    </div>
  </nav>
</header>