nav.php

<nav class="navbar navbar-expand-lg " style="background-color: #d3d3d3;">
  <div class="container-fluid">
    <a class="navbar-brand" href="index.php"><i class="bi bi-house-door-fill"></i> Home</a>
      <ul class="navbar-nav">
        <?php if(!isset($_SESSION['id'])){ ?>
        <li class="nav-item">
          <a class="nav-link" aria-current="page" href="login.php"><i class="bi bi-pencil-square"></i> เข้าสู่ระบบ</a>
        </li> 
        <?php }else{?>  
            <li class="nav-item dropdown">
          <a class="btn btn-outline-secondary btn-sm dropdown-toggle" href="#" role="button" data-bs-toggle="dropdown" aria-expanded="false">
          <i class="bi bi-person-lines-fill"></i> <?php echo $_SESSION['username'];?>
          </a>
          <ul class="dropdown-menu">
          <?php if(isset($_SESSION['id'])&&$_SESSION['role']=='a'){?>
            <li><a class="dropdown-item" href="category.php"><i class="bi bi-bookmarks"></i> จัดการหมวดหมู่</a></li>
            <li><a class="dropdown-item" href="#"><i class="bi bi-person-check"></i> จัดการผู้ใช้งาน</a></li>
            <?php } ?>
            <li><a class="dropdown-item" href="logout.php"><i class="bi bi-power"></i> ออกจากระบบ</a></li>
          </ul>
        </li>
            <?php } ?>
      </ul>
  </div>
</nav>