cakephp管理员前缀资产

I want have cakephp app with 2 part the main site and the admin panel and layout and design of the 2 part are seprate

I created Admin prefix and put my admins controller and template file in Admin folder

I created a folder in webroot named Admin too and put my admin related assets there .

In cakephp config/App.php there is part to specify base url of assets . i's look like this

'App' => [
    'namespace' => 'App',
    'encoding' => env('APP_ENCODING', 'UTF-8'),
    'defaultLocale' => env('APP_DEFAULT_LOCALE', 'en_US'),
    'base' => false,
    'dir' => 'src',
    'webroot' => 'webroot',
    'wwwRoot' => WWW_ROOT,
    // 'baseUrl' => env('SCRIPT_NAME'),
    'fullBaseUrl' => false,
    'imageBaseUrl' => '',
    'cssBaseUrl' => 'css/',
    'jsBaseUrl' => 'js/',
    'paths' => [
        'plugins' => [ROOT . DS . 'plugins' . DS],
        'templates' => [APP . 'Template' . DS],
        'locales' => [APP . 'Locale' . DS],
    ],
],

I'm wondering how can i specify defferent dicrectory for assets for Admin ?

Or how should i call css method in Html helper for admin ?

I load css file in main part of site like this

<?= $this->Html->css('custom.css') ?>

But i have to load it for admin side like this

<?= $this->Html->css('../Admin/css/custom.css') ?>

Is there any way i can fix this and load it like i do the main part ?

I also used it like this but it seems not to recognize prefix option

<?= $this->Html->css('custom.css' , ['prefix'=>'Admin']) ?>