Thanks for the explanation and fix; System Preferences indeed has it set to dark.

Sanity has been restored.

Hmm-m, I took a second look at the code. Since first-time visitors probably won't even notice the "moon" button, this site will recognize the visitor's system preference for dark mode. However, if you override it with the "sun" button, your choice will be remembered. You can reset your overridden choice by clearing cookies.

The practical consequence is that visitors on mobile phones using "dark mode" in their settings will automatically get it here without having to bonk a button that they may not have even realized existed.