Since Confluence 9.1, the default theme has been set to "Match System". With many end-users using dark mode in their browsers/OS, Confluence ends up set to dark theme by default which may cause problems with customized interfaces as per its documentation. This can be particularly problematic for instances open to anonymous users as they cannot chose a different theme.
This feature request aims to allow Confluence administrators to set the default theme. This way, instances that rely on customized themes can be kept in light theme regardless of the end-user's system theme.
Suggestion