navbar bootstrap v4 fix

1<nav class="navbar navbar-expand-sm navbar-dark fixed-top bg-dark">
2  <div class="container">
3    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
4    </button>
5    <a class="navbar-brand" href="/">Application name</a>
6    <div class="navbar-collapse collapse" id="navbarSupportedContent">
7      <ul class="nav navbar-nav mr-auto">
8        <li class="nav-item"><a href="/" class="nav-link">Home</a></li>
9        <li class="nav-item"><a href="/Home/About" class="nav-link">About</a></li>
10        <li class="nav-item"><a href="/Home/Contact" class="nav-link">Contact</a></li>
11      </ul>
12
13      <ul class="nav navbar-nav navbar-right mr-auto">
14        <li class="nav-item"><a href="/Account/Register" id="registerLink" class="nav-link">Register</a></li>
15        <li class="nav-item"><a href="/Account/Login" id="loginLink" class="nav-link">Log in</a></li>
16      </ul>
17
18    </div>
19  </div>
20</nav>

1<nav className="fixed-top">