<nav>
    <ul>
        <li><a class="<?= $page == "intro" ? "selected" : ""; ?>" href="?page=multipage&subpage=intro">Intro</a></li>
        <li><a class="<?= $page == "print-server" ? "selected" : ""; ?>" href="?page=multipage&subpage=print-server">Print $_SERVER</a></li>
        <li><a class="<?= $page == "print-get" ? "selected" : ""; ?>" href="?page=multipage&subpage=print-get">Print $_GET</a></li>
        <li><a class="<?= $page == "server-lengths" ? "selected" : ""; ?>" href="?page=multipage&subpage=server-lengths">SERVER LENGTHS</a></li>
    </ul>
</nav>
