RewriteEngine On

RewriteCond %{REQUEST_URI} !^/.*\.css$
RewriteCond %{REQUEST_URI} ^/page/$
RewriteRule ^page/$ index.php?page=criticalError [L,NS]

RewriteCond %{REQUEST_URI} !^/.*\.css$
RewriteCond %{REQUEST_URI} ^/page/[a-zA-Z]+/$
RewriteRule ^page/([a-zA-Z]+)/$ index.php?page=$1 [L,NS]