To run HtmGem — after having copied the files — there is nothing to do but to add the URL rewriting rules.
# This text must be placed in the server's configuration index index.gmi index.php index.html rewrite ^(.+\.gmi)$ htmgem/index.php?rw=1&url=$1;
# This text can be placed at the root of the web site in a file ".htaccess". DirectoryIndex index.gmi index.php index.html RewriteEngine on RewriteRule ^(.+\.gmi)$ htmgem/index.php?rw=1&url=$1
Afterwards,
Add additional styles as a link parameter or adapt the text decoration: