syntax error, unexpected '=>' (T_DOUBLE_ARROW)

<?php
use think\facade\Env;
// 错误页面模板
'http_exception_template' => [
    // 404 错误重定向到 404.php
    404 => $_SERVER['DOCUMENT_ROOT'].'/404.php',
],
// +----------------------------------------------------------------------
// | ThinkPHP [ WE CAN DO IT JUST THINK ]
// +----------------------------------------------------------------------
// | Copyright (c) 2006~2018 http://thinkphp.cn All rights reserved.
// +----------------------------------------------------------------------
// | Licensed ( http://www.apache.org/licenses/LICENSE-2.0 )
// +----------------------------------------------------------------------
// | Author: liu21st <liu21st@gmail.com>
// +----------------------------------------------------------------------

// +----------------------------------------------------------------------
// | 应用设置