Htaccess joomla subdomain index.html. How to setup?

Question

Joomla

There is a main site directory main. It contains two more site and subdomain directories. The site directory contains joomla. In the subdomain directory, the usual index.html.
In the admin panel on the hosting, the binding looks like this:
For the main site main-domain.ru -> main/site
For the subdomain sub.main-domain.ru -> main/
subdomain index.php from main/site only nothing works and layout without styles, etc.
I need that when entering a subdomain, the usual index.html is taken as the basis, which lies in site / subdomain without mentioning joomla.
As for the htaccess file itself, it remains original from joomla

########## Begin - Joomla! core SEF Section
#
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !^/index.php
RewriteCond %{REQUEST_URI} (/|\.php|\.html|\.htm|\.feed|\.pdf|\.raw|/[^.]*)$  [NC]
RewriteCond %{HTTP_HOST} !^sub.main-domain.ru
RewriteRule (.*) index.php
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization},L]
#
########## End - Joomla! core SEF Section

Answer 1

in .htaccess, at the very bottom, before
add:

RewriteCond %{HTTP_HOST} !^sub.main-domain.ru  [OR,NC]