Wordpress查找根文件并添加自定义代码

I am trying to add some custom code in WordPress site. I can not find the root file. It seems it's the index.php in the root because when I delete it the site goes down. However, when I put my custom code in there I can't see it. Not even html. Is the htaccess overriding or what's going on here?

Here is the htacess file code:

# BEGIN NON_LSCACHE
## LITESPEED WP CACHE PLUGIN - Do not edit the contents of this block! ##
### marker MINIFY start ###
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{DOCUMENT_ROOT}%{REQUEST_URI} ^(.*)/min/(\w+)\.(css|js)$
RewriteCond %1/wp-content/cache/$2/$1.$2 -f
RewriteRule min/(\w+)\.(css|js) wp-content/cache/$2/$1.$2 [L]
</IfModule>
### marker MINIFY end ###

## LITESPEED WP CACHE PLUGIN - Do not edit the contents of this block! ##
# END NON_LSCACHE
# BEGIN LSCACHE
## LITESPEED WP CACHE PLUGIN - Do not edit the contents of this block! ##
<IfModule LiteSpeed>
RewriteEngine on
CacheLookup on
RewriteRule .* - [E=Cache-Control:no-autoflush]
RewriteRule ^min/\w+\.(css|js) - [E=cache-control:no-vary]

### marker CACHE RESOURCE start ###
RewriteRule wp-content/.*/[^/]*(responsive|css|js|dynamic|loader|fonts)\.php - [E=cache-control:max-age=3600]
### marker CACHE RESOURCE end ###

### marker FAVICON start ###
RewriteRule favicon\.ico$ - [E=cache-control:max-age=86400]
### marker FAVICON end ###

</IfModule>
## LITESPEED WP CACHE PLUGIN - Do not edit the contents of this block! ##
# END LSCACHE

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress