How to fix permissions on wordpress docker file system

docker ps (to find docker container name)
docker exec -t -i mycontainer /bin/bash
cd .. (so you see the html folder)
chown -R www-data:www-data html

Or the following commands(first one takes care of above, bottom two may or may not be needed)

docker exec -it <container_name_or_id> chown -R www-data:www-data /var/www/html

docker exec -it <container_name_or_id> find /var/www/html -type d -exec chmod 755 {} \;

docker exec -it <container_name_or_id> find /var/www/html -type f -exec chmod 644 {} \;