Breeze Wiki offers three different theme options: Dark, Light, and Default.

Default appears to be either light or dark depending on the theme of
the OG Fandom page.

Instead of Default, an Auto theme that is dark or light based on
browser/system theme would be lovely.

Thank you for making Breeze Wiki a reality.

Sorry, can't be done due to technical limitations!

In addition, some wikis have broken styling and unreadable text on their 
non-default schemes, since they haven't been thoroughly checked. If 
"auto" was an option, then some wikis loaded using the alternate styling 
would be broken by default, which wouldn't be pleasant.

I suggest just clicking light or dark on each of your devices to match 
its system theme.