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Excel 2016: All cells dark by default

I have a very weird and annoying problem. Cells in my Excel 2016 are dark by default. Every new document is dark. Every opened document is dark (sometimes with some exceptions).

I tried removing the formatting. Macros seem to not be working as well… I have an idea though what’s causing it. It might be the Windows’ custom dark theme which I installed. It’s not causing problems in the system. I think that it might be just Excel trying to adjust its theme to my Windows’ theme.

Can I stop it from using my Windows’ theme if that’s why it’s all dark? I could of course fill the cells with the white color and the change the text color to black but then I would have to do it manually every time… Also, going to “Page Layout” tab and changing there colors, fonts, themes or effects does not have any effect. Even the custom colors are not working. Why is it happening? Please help. I’m very new to Excel and I have just basic knowledge of it.
Screenshot of what’s happening: Excel – dark cells