RewriteEngine on
RewriteBase /
DirectoryIndex frontend/www/index.php
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} cpanel/(.*)$
# Why not "-f" - because it's domain of 3d level: VirtualDocumentRoot /path/to/htdocs/%-3/ and if I use "-f" file not founds :(
RewriteCond backend/www/%1 -F
RewriteRule . backend/www/%1 [L]
RewriteCond %{REQUEST_URI} cpanel/(.*)$
RewriteCond backend/www/%1 !-F
RewriteRule . backend/www/index.php?b=%1 [L]
RewriteCond %{REQUEST_URI} !cpanel/(.*)$
RewriteCond frontend/www%{REQUEST_URI} -F
RewriteRule . frontend/www%{REQUEST_URI}
RewriteCond %{REQUEST_URI} !cpanel/(.*)$
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule . frontend/www/index.php?f=%{REQUEST_URI}
.
├── .htaccess (with code I provided)
├── frontend
│ ├── www
│ ├── css
│ │ ├── base.css
│ └── index.php
├── backend
├── www
├── css
│ ├── base.css
└── index.php