Navbar

<nav class="navbar navbar-expand-xl navbar-light bg-light py-0">
  <a class="navbar-brand" href="#">Navbar</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#nav1" aria-controls="nav1" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <div class="collapse navbar-collapse" id="nav1">
    <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 dropdown">
        <a class="nav-link dropdown-toggle" href="#" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false" id="dropdown1">Dropdown</a>
        <div class="dropdown-menu" aria-labelledby="dropdown1">
          <a class="dropdown-item" href="#">Action</a>
          <a class="dropdown-item" href="#">Another action</a>
          <a class="dropdown-item" href="#">Something else here</a>
        </div>
      </li>
    </ul>
    <form class="form-inline my-2 my-lg-0">
      <input class="form-control form-control-sm mr-sm-2" type="search" placeholder="Search" aria-label="Search">
      <button class="btn btn-sm my-2 my-sm-0 btn-outline-secondary" type="submit">Search</button>
    </form>
  </div>
</nav>

<nav class="navbar navbar-expand-xl navbar-dark bg-dark py-0">
  <a class="navbar-brand font-weight-normal ls-2" href="../index.html">RE<span class="navbar-brand-i">!</span>GN</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#nav2" aria-controls="nav2" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <div class="collapse navbar-collapse" id="nav2">
    <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 dropdown">
        <a class="nav-link dropdown-toggle" href="#" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false" id="dropdown2">Dropdown</a>
        <div class="dropdown-menu" aria-labelledby="dropdown2">
          <a class="dropdown-item" href="#">Action</a>
          <a class="dropdown-item" href="#">Another action</a>
          <a class="dropdown-item" href="#">Something else here</a>
        </div>
      </li>
    </ul>
    <form class="form-inline my-2 my-lg-0">
      <input class="form-control form-control-sm mr-sm-2" type="search" placeholder="Search" aria-label="Search">
      <button class="btn btn-sm my-2 my-sm-0 btn-outline-secondary" type="submit">Search</button>
    </form>
  </div>
</nav>

<nav class="navbar navbar-expand-xl navbar-dark bg-primary py-0">
  <a class="navbar-brand font-weight-normal ls-2" href="../index.html">RE<span class="navbar-brand-i">!</span>GN</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#nav3" aria-controls="nav3" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <div class="collapse navbar-collapse" id="nav3">
    <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 dropdown">
        <a class="nav-link dropdown-toggle" href="#" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false" id="dropdown3">Dropdown</a>
        <div class="dropdown-menu" aria-labelledby="dropdown3">
          <a class="dropdown-item" href="#">Action</a>
          <a class="dropdown-item" href="#">Another action</a>
          <a class="dropdown-item" href="#">Something else here</a>
        </div>
      </li>
    </ul>
    <form class="form-inline my-2 my-lg-0">
      <input class="form-control form-control-sm mr-sm-2" type="search" placeholder="Search" aria-label="Search">
      <button class="btn btn-sm my-2 my-sm-0 btn-outline-light" type="submit">Search</button>
    </form>
  </div>
</nav>