Answers for "two navbar in bootstrap 4"

bootstrap 4 navbar

<nav class="navbar navbar-expand-lg navbar-light bg-light">
  <a class="navbar-brand" href="#">Navbar</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>

  <div class="collapse navbar-collapse" id="navbarSupportedContent">
    <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 dropdown">
        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          Dropdown
        </a>
        <div class="dropdown-menu" aria-labelledby="navbarDropdown">
          <a class="dropdown-item" href="#">Action</a>
          <a class="dropdown-item" href="#">Another action</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="#">Something else here</a>
        </div>
      </li>
      <li class="nav-item">
        <a class="nav-link disabled" href="#">Disabled</a>
      </li>
    </ul>
    <form class="form-inline my-2 my-lg-0">
      <input class="form-control mr-sm-2" type="search" placeholder="Search" aria-label="Search">
      <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
    </form>
  </div>
</nav>

bootstrap 4 navbar

<!-- Bootstrap 4.6 Navbar -->
<nav class="navbar navbar-expand-lg navbar-light bg-light">
   <a class="navbar-brand" href="#">Navbar</a>
   <button
      class="navbar-toggler"
      type="button"
      data-toggle="collapse"
      data-target="#navbarSupportedContent"
      aria-controls="navbarSupportedContent"
      aria-expanded="false"
      aria-label="Toggle navigation"
   >
      <span class="navbar-toggler-icon"></span>
   </button>

   <div class="collapse navbar-collapse" id="navbarSupportedContent">
      <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 dropdown">
            <a
               class="nav-link dropdown-toggle"
               href="#"
               id="navbarDropdown"
               role="button"
               data-toggle="dropdown"
               aria-haspopup="true"
               aria-expanded="false"
            >
               Dropdown
            </a>
            <div class="dropdown-menu" aria-labelledby="navbarDropdown">
               <a class="dropdown-item" href="#">Action</a>
               <a class="dropdown-item" href="#">Another action</a>
               <div class="dropdown-divider"></div>
               <a class="dropdown-item" href="#">Something else here</a>
            </div>
         </li>
         <li class="nav-item">
            <a
               class="nav-link disabled"
               href="#"
               tabindex="-1"
               aria-disabled="true"
               >Disabled</a
            >
         </li>
      </ul>
      <form class="form-inline my-2 my-lg-0">
         <input
            class="form-control mr-sm-2"
            type="search"
            placeholder="Search"
            aria-label="Search"
         />
         <button class="btn btn-outline-success my-2 my-sm-0" type="submit">
            Search
         </button>
      </form>
   </div>
</nav>