我希望我的導(dǎo)航欄圖標(biāo)在用戶位于某個頁面時（例如在 instagram 等）上改變顏色。這就是我嘗試過的 - bottomBar.php：if ($page == 'friends') { $theme = 'link_friendsWall_active'; $theme2 = 'link_index'; $theme3 = 'link_trophypage'; $theme4 = 'link_selfpage';} else if ($page == 'index') { $theme = 'link_friendsWall'; $theme2 = 'link_index_active'; $theme3 = 'link_trophypage'; $theme4 = 'link_selfpage';} else if ($page == 'trophy') { $theme = 'link_friendsWall'; $theme2 = 'link_index'; $theme3 = 'link_trophypage_active'; $theme4 = 'link_selfpage';} else if ($page == 'profile') { $theme = 'link_friendsWall'; $theme2 = 'link_index'; $theme3 = 'link_trophypage'; $theme4 = 'link_selfpage_active';}$page 是指在 index.php（作為索引）、friendsWall.php（作為朋友）等文件中定義的變量，其中包含 bottom_menu。主題定義的變量是在 css 中設(shè)置樣式的類。然后在我的底部菜單中，我調(diào)用了這些變量：<div class="bottom_menu">    <li><a class="<?=$theme?>" href="includes/handlers/friends_link.php">            <i class="fas fa-user-friends"></i>        </a></li>    <li><a class="<?=$theme2?>" href="index.php">            <i class="fas fa-users "></i>        </a></li>    <li><a href="#">            <i class="fas fa-plus-circle"></i>        </a></li>    <li><a class="<?=$theme3?>" href="trophyPage.php">            <i class="fas fa-trophy"></i>        </a></li>    <li><a class="<?=$theme4?>" href="myProfile.php">            <img class='img_bottom_bar' src="<?php echo $user['profile_pic']; ?>" width="30px" height="30px" border-radius="20px">        </a></li></div>我的問題是該網(wǎng)站沒有從其他頁面讀取變量 $page 。索引.php：  session_start();  include("includes/header.php");  include("includes/bottomBar.php"); include("includes/classes/User.php"); include("includes/classes/Post.php"); $page = 'index';