<nav class="navbar navbar-expand-md fixed-top">
    <div class="container">
        <a class="navbar-brand" href="#">FP</a>
        <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarsExampleDefault" aria-controls="navbarsExampleDefault" aria-expanded="false" aria-label="Toggle navigation">
        <span class="navbar-toggler-icon"></span>
      </button>

        <div class="collapse navbar-collapse" id="navbarsExampleDefault">
            <ul class="navbar-nav mr-auto">
                <li class="nav-item">
                    <a class="nav-link" href="index.php">Home</a>
                </li>
                <li class="nav-item">
                    <a class="nav-link" href="products.php">Products</a>
                </li>
                <li class="nav-item">
                    <a class="nav-link" href="cart.php">View Cart</a>
                </li>
                <li class="nav-item">
                    <a class="nav-link" href="account.php">Sign up</a>
                </li>
                <li class="nav-item dropdown">
                    <a class="nav-link dropdown-toggle" href="#" id="dropdown01" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">Sign in</a>
                    <div class="dropdown-menu" aria-labelledby="dropdown01">
                        <form class="form-inline" method="post" action="login.php">
                            <fieldset>
                                <!-- Text input-->
                                <div class="form-group">
                                    <input id="login_usr" name="login_usr" type="text" placeholder="username" class="form-control input-md" required="">
                                </div>

                                <!-- Password input-->
                                <div class="form-group">
                                    <input id="login_pwd" name="login_pwd" type="password" placeholder="password" class="form-control input-md" required="">
                                </div>

                                <!-- Button -->
                                <div class="form-group">
                                    <button id="login_submit" value="submit" class="btn btn-primary">Log in</button>
                                </div>

                            </fieldset>
                        </form>
                    </div>
                </li>
            </ul>
        </div>
    </div>
</nav>