Octoprint UI has changed to dark

A couple of weeks ago, my Octoprint UI changed to a dark theme. I find it very hard to read dark red text on a dark grey background, and muddy blue buttons with black text are unreadable.

Everything I have googled talks about TouchUI (I'm not using it, it isn't installed) or Themeify (I don't use it, it's not installed).
Something must have changed but I don't recall changing anything and I thought at the time "I'll deal with it later" - a mistake, I should have addressed it while it was fresh in my mind.

The Appearance tab has no way to change the colours that I can see - the Colour drop down doesn't change anything.

How can I get back to white with black text, please?

Start in safe mode, then figure out what plugin is causing this (because it has to be a plugin you installed, UI Customizer could also be an option, OctoPrint stock only ships with a light theme) and uninstall/deactivate/modify it to your liking.

Many thanks, I will try that

Eventually reimaged and all is now fine. Maybe something was corrupted.
Many thanks for your help.