Fix styling for login pages for dark mode users

[hotzenklotz]

This PR fixes some styling issues for dark mode users after logging out. The default theme for WEBKNOSSOS is light, especially when logged out. This fix, restores light mode on each log out to fix the UI. Theme switching in this case is not persisted as a user choice, though, in order to return to dark mode on the next login for dark mode users.

URL of deployed dev instance (used for testing):

• https://___.webknossos.xyz

Steps to test:

1. Log in
2. Switch to dark mode
3. Log out.
4. Login page should look correct, i.e. have hints for each input field
5. Log in again. You should be in dark mode once more.

Issues:

• fixes Login Screen has no input hints in dark mode #6885

---

(Please delete unneeded items, merge only when none are left open)

• Updated changelog
• Updated migration guide if applicable
• Updated documentation if applicable
• Adapted wk-connect if datastore API changes
• Adapted wk-libs python client if relevant API parts change
• Removed dev-only changes like prints and application.conf edits
• Considered common edge cases
• Needs datastore update after deployment

[philippotto]

This PR fixes some styling issues for dark mode users after logging out.

In Firefox, I have the styling problem simply by opening the log in page (without having logged in before). See screenshot. I think, the problem is that the default theme is "auto" and my Firefox uses a dark theme which then propagates to wK using the dark theme.

Maybe it would be easier to give the entire log in view a css class à la "light-container" and then override the input color via .light-container { input { color: black; } } or something like that. With the current approach I would also suspect that logging out and directly logging in again could lose the theme setting (not tested, though).

[philippotto]

👍