RewriteEngine On
RewriteCond %{HTTP:X-Forwarded-Proto} !https
SetEnvIf X-Forwarded-Proto "https" HTTPS=on
RewriteCond %{HTTPS} !=on
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d 
RewriteCond %{REQUEST_FILENAME}\.html -f
RewriteRule ^(.*)$ $1.html [NC,L]