navegacion.php

<nav class="navbar navbar-expand-md bg-dark navbar-dark mb-4">        
    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#collapsibleNavbar">
        <span class="navbar-toggler-icon"></span>
    </button>
    <div class="collapse navbar-collapse " id="collapsibleNavbar">
        <ul class="navbar-nav nav-fill w-100">

            <li class="nav-item dropdown">
                <a href="" class="nav-link dropdown-toggle" id="navbardrop" data-toggle="dropdown">
                    -Productos-
                </a>
                <div class="dropdown-menu text-center"  style="width: 100%;">
                    <a href="consulta_productos.php" class="dropdown-item">-Consultar-</a>
                    <a href="altas_productos.php" class="dropdown-item">-Dar de alta-</a>
                    <a href="modificar_productos.php" class="dropdown-item">-Modificar-</a>
                </div>
            </li>
            <li class="nav-item dropdown">
                <a href="" class="nav-link dropdown-toggle" id="navbardrop" data-toggle="dropdown">
                    -Entradas-
                </a>
                <div class="dropdown-menu text-center"  style="width: 100%;">
                    <a href="nueva_entrada.php" class="dropdown-item">-Nueva entrada-</a>
                    <a href="consultar_entradas.php" class="dropdown-item">-Consultar entrdas-</a>                    
                </div>
            </li>
            
            <li class="nav-item dropdown">
                <a href="" class="nav-link dropdown-toggle" id="navbardrop" data-toggle="dropdown">
                    -Salidas-
                </a>
                <div class="dropdown-menu text-center"  style="width: 100%;">
                    <a href="nueva_salida.php" class="dropdown-item">-Nueva salida-</a>
                    <a href="consultar_salidas.php" class="dropdown-item">-Consultar salidas-</a>
                </div>
            </li>
            <li class="nav-item dropdown">
                <a href="" class="nav-link dropdown-toggle" id="navbardrop" data-toggle="dropdown">
                    -Traspasos-
                </a>
                <div class="dropdown-menu text-center"  style="width: 100%;">
                    <a href="nuevo_traslado.php" class="dropdown-item">-Nuevo traspaso-</a>
                    <a href="consultar_traspasos.php" class="dropdown-item">-Consultar traspasos-</a>  
                </div>
            </li>

        <li class="nav-item">
            <a class="nav-link" href="almacenes.php">-Almacenes-</a>
        </li>        
        
        </ul>
    </div>  
</nav>