Collabora Online not respecting theme

[igbjnI05bF]

Describe the Bug

Collabora online, latest version in Debian 12 repos, is not always respecting the Nextcloud theme which is set to the light theme. The dark theme is completely unreadable for spreadsheets, I want to force light theme for all users in Nextcloud. Currently it seems like certain browsers are opening in dark theme by default.

Nextcloud 28.0.5
Collabora Online Development Edition 24.04.1.3 89a7742
Nextcloud Light theme is selected and user theming is disabled

Steps to Reproduce

I can reproduce this every time on my android phone by doing the following:

1. Share a spreadsheet file via a public link in Nextcloud
2. Open that public link (not signed in - anonymous) on Android using Firefox 125.0b9
3. Witness this open in dark mode by default (with unreadable text)

This isn't the only time I've seen it open in dark mode, I've had many people reach out to me about this. It may only be anonymous links though, it's possible that when signed in the Nextcloud settings are correctly forcing light theme.

Expected Behavior

I want Collabora to always be light mode. I wish I could just disable dark mode entirely. It makes documents unreadable in many situations.