Remove .html extension from URL only in root - .htaccess

Question

I'm trying to remove the .html file extension from my URL's to make them look nicer. I've seen many examples of this and have tried them, but I'm struggling to find something that only works in the root, and doesn't apply to any subdirectories or subdomains.
Can I get any help with this?
Example:
example.org/test.html > example.org/test
example.org/food/xyz.html > example.org/food/xyz.html
login.example.org/something.html > login.example.org/something.html

Answer 1

Your question is a bit vague, so I will concentrate on the main issue you mention:
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !/.+\.html
RewriteRule ^/?([^/]+)$ $1.html [L]
Alternative approach:
RewriteEngine on
RewriteCond %{REQUEST_FILENAME}.html -f
RewriteRule ^/?([^/]+)$ $1.html [L]
If this is limited to only a single host name (as your examples might suggest) depends on your setup. Such thing is easiest done if you place the rule in the real host configuration of your http server instead of using .htaccess style files. That is also why I append a general hint:
You should always prefer to place such rules inside the http servers host configuration instead of using .htaccess style files. Those files are notoriously error prone, hard to debug and they really slow down the server. They are only provided as a last option for situations where you do not have control over the host configuration (read: really cheap hosting service providers) or if you have an application that relies on writing its own rewrite rules (which is an obvious security nightmare).
In the comment you wrote that you also want to force the shorter notation, so redirect users request a URL with such "file name extension" to the version without.
I don't really see any point in this, but it certainly is possible:
RewriteEngine on
RewriteCond %{ENV:REDIRECT_STATUS} !^.
RewriteRule ^. - [L]
RewriteCond %{REQUEST_URI} ^/.+\.html$
RewriteCond %{REQUEST_FILENAME} -f
RewriteRule ^/?(.+)\.html$ /$1 [L,R=301]
RewriteCond %{REQUEST_URI} !^/.+\.html$
RewriteCond %{REQUEST_FILENAME}.html -f
RewriteRule ^/?([^/]+)$ /$1.html [L]