I'm using a theme to make the Firefox UI a dark gray color. Previously, when I launched settings or about:config, it was all black. When I started Firefox 96 for the first time just now, it popped up some auto theming thing where I promptly clicked the option to set it back to the theme I was previously using, and now the settings and about:config menus are a white background. Is there a setting to change these back to a black background without changing my entire theme? I've tried digging around in settings and am not seeing anything.
layout.css.prefers-color-scheme.content-override from 3 to 2 as per the link provided by /u/thermalzombie solved my problem. My Firefox is set to a gray theme but my Windows system theme is dark mode so it switched from setting the those backgrounds based on my Windows theme to based on my Firefox theme.