The file `themes.gitconfig` is not meant to be installed in `/etc/delta`; it's
meant to be installed in `/usr/share/delta`. It even says, in the
example at the top of the file:

This file is not system configuration, it's a resource file that users
can include. Users shouldn't edit this file; if they want to write their
own theme, they can trivially do so in their `~/.gitconfig`, perhaps by
copy-pasting one of the examples from that file to start with.

Hi Josh,

Quoting Josh Triplett (2025-09-17 14:54:46)
packaging provides the file *both* as a system-wide configuration file
and (via a symlink) from the upstream documented path.

I disagree that Debian users must copy the file to customize it: The
choice of offering it it for system-wide editing was deliberate.

Kind regards,

 - Jonas

That is an annoying and entirely unnecessary divergence from upstream.
That is not going to "work" anywhere other than Debian, and it's a
gratuitous point of indirection from what is supposed to be a fixed
resource file users can include. It'd be obnoxious for a sysadmin on a
multi-user system to make such an edit to a file that users'
configurations will expect to match upstream, and on a single-user
system it's pointless to do so rather than just setting up your own git
configuration.

This seems like the equivalent of symlinking /usr/share/dict/words to
/etc/words so sysadmins can edit the system wordlist, rather than having
users add entries to their personal spelling corrections lists.