codeigniter/
├── application/
├── composer.json
├── composer.lock
├── public/
|   ├── themes/
|   |     └── Default
|   |         └── views  
|   |             ├── partial 
|   |             └── layouts  
│   ├── .htaccess
│   └── index.php
└── vendor/
    └── codeigniter/
        └── framework/
            └── system/

I custom view helper of codeigniter 4 framework to config the theme with Code Modules SEE THE IMAGE ==> Layout of Theme

Install:

composer require fireantlabs/fatheme

Go application -> Config -> Autoload.php

$psr4 = ['Theme' =>FCPATH.'themes']

Config eviroment to development --> Show debug bar

$_SERVER['CI_ENVIRONMENT'] = 'development';