<header>
     <div class="logo">Over The Garden Wall</div>
     <nav>
          <ul>
               <li>
                    <a href="./" class="<?php if ($page_id == 1) echo 'active'; ?>">Home</a>
               </li>
               <li>
                    <a href="./index.php?id=2" class="<?php if ($page_id == 2) echo 'active'; ?>">Characters</a>
               </li>
               <li>
                    <a href="./index.php?id=3" class="<?php if ($page_id == 3) echo 'active'; ?>">Episodes</a>
               </li>
          </ul>
     </nav>
</header>