Hosting 2 web with different root dir

so i am running mrtg on my rpi.
at the same time i am installing pihole.

pihole rewrite my lighttpd.conf change root dir from /var/www/ to /var/www/html.
It cause stop my mrtg.
if i edit root dir back to /var/www, mrtg is running, but pihole stop.

how to fix it?
i have read this still dont have clue how to fix it.