I tried changing the stylesheet to Positoron, but it doesn't render.

I have done all the steps as described in this guide and confirmed that it works fine.
Note that since naciscdn.org is down, I have replaced the relevant part of external-data.yml with the following description.
https://naturalearth.s3.amazonaws.com/110m_cultural/ne_110m_admin_0_boundary_lines_land.zip.

I would like to use the Positoron style for my basemap. I downloaded the style sheet from here and rewrote /usr/local/etc/renderd.conf.

[renderd]
num_threads=8
tile_dir=/var/lib/mod_tile
stats_file=/var/run/renderd/renderd.stats

[mapnik]
plugins_dir=/usr/lib/mapnik/3.0/input
font_dir=/usr/share/fonts/truetype
font_dir_recurse=1

[ajt]
URI=/hot/
TILEDIR=/var/lib/mod_tile
XML=/home/ubuntu/basemap-styles/cartocss/web-styles/positron.tm2/project.xml
HOST=localhost
TILESIZE=256

When I start the renderd daemon and try to access http://myhost/hot/0/0/0.png, I just get a gray image and it does not render correctly.
When I try to access the site again after some time has passed, I just get a gray image.
There are no errors in the renderd daemon log.
In the /var/lib/mod_tile/ajt/ directory, a .meta file has been created.

renderd[58068]: DEBUG: Got incoming connection, fd 5, number 1
renderd[58068]: DEBUG: Got incoming request with protocol version 2
renderd[58068]: DEBUG: Got command RenderPrio fd(5) xml(ajt), z(0), x(0), y(0), mime(image/png), options()
renderd[58068]: DEBUG: START TILE ajt 0 0-0 0-0, new metatile
renderd[58068]: Rendering projected coordinates 0 0 0 -> -20037508.342800|-20037508.342800 20037508.342800|20037508.342800 to a 1 x 1 tile
renderd[58068]: DEBUG: DONE TILE ajt 0 0-0 0-0 in 0.005 seconds
debug: Creating and writing a metatile to /var/lib/mod_tile/ajt/0/0/0/0/0/0.meta

renderd[58068]: DEBUG: Sending render cmd(3 ajt 0/0/0) with protocol version 2 to fd 5
renderd[58068]: DEBUG: Connection 0, fd 5 closed, now 0 left

Please let me know what action I have to take in order to use Positoron style.