menu.php

<nav class="navbar navbar-default">
    <div class="container-fluid">

        <ul class="nav navbar-nav navbar-left">
            <li><a href="/">Home</a></li>
            <li><a href="/empresa">Empresa</a></li>
            <li><a href="/produtos">Produtos</a></li>
            <li><a href="/servicos">Serviços</a></li>
            <li><a href="/contato">Contato</a></li>
            <li><a href="/admin">Admin</a></li>
        </ul>
        <form class="navbar-form navbar-right" method="post" action="busca">
            <div class="input-group">
            <input type="text" class="form-control" name="busca" placeholder="Busca..." required>
            <span class="input-group-btn">
                <button type="submit" class="btn btn-flat"><i class="glyphicon glyphicon-search"></i>
                </button>
            </span>
            </div>
        </form>
    </div>
</nav>