Hmm, it should be. Are you sure you have app dark mode enabled on your machine ? https://uk.pcmag.com/news-analysis/122487/how-to-enable-dark-mode-in-windows-10
Bug 1588548 Comment 1 Edit History
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Hmm, it should be adhering to the OS dark mode. Are you sure you have app dark mode enabled on your machine ? https://uk.pcmag.com/news-analysis/122487/how-to-enable-dark-mode-in-windows-10