bootstrap responsive navigation menu

1<section id="headnev" class="navbar navbar-fixed-top">  

1<nav class="navbar navbar-expand-lg navbar-light bg-light">
2  <a class="navbar-brand" href="#">Navbar</a>
3  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
4    <span class="navbar-toggler-icon"></span>
5  </button>
6
7  <div class="collapse navbar-collapse" id="navbarSupportedContent">
8    <ul class="navbar-nav mr-auto">
9      <li class="nav-item active">
10        <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
11      </li>
12      <li class="nav-item">
13        <a class="nav-link" href="#">Link</a>
14      </li>
15      <li class="nav-item dropdown">
16        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
17          Dropdown
18        </a>
19        <div class="dropdown-menu" aria-labelledby="navbarDropdown">
20          <a class="dropdown-item" href="#">Action</a>
21          <a class="dropdown-item" href="#">Another action</a>
22          <div class="dropdown-divider"></div>
23          <a class="dropdown-item" href="#">Something else here</a>
24        </div>
25      </li>
26      <li class="nav-item">
27        <a class="nav-link disabled" href="#">Disabled</a>
28      </li>
29    </ul>
30    <form class="form-inline my-2 my-lg-0">
31      <input class="form-control mr-sm-2" type="search" placeholder="Search" aria-label="Search">
32      <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
33    </form>
34  </div>
35</nav>

1<nav class="navbar navbar-expand-lg navbar-light bg-light">
2  <a class="navbar-brand" href="#">Navbar</a>
3  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNavAltMarkup" aria-controls="navbarNavAltMarkup" aria-expanded="false" aria-label="Toggle navigation">
4    <span class="navbar-toggler-icon"></span>
5  </button>
6  <div class="collapse navbar-collapse" id="navbarNavAltMarkup">
7    <div class="navbar-nav">
8      <a class="nav-item nav-link active" href="#">Home <span class="sr-only">(current)</span></a>
9      <a class="nav-item nav-link" href="#">Features</a>
10      <a class="nav-item nav-link" href="#">Pricing</a>
11      <a class="nav-item nav-link disabled" href="#">Disabled</a>
12    </div>
13  </div>
14</nav>