But we do get the "prefers-color-scheme"[0] and "color-scheme"[1] CSS media features, they make it easy for everyone, the visitor can just change the OS/Browser theme and the browser tells the website about what color the visitor prefers. It's up to the developer to ignore/accept their preference.
This is an accessibility thing, many hates dark theme, and some cannot look at a bright screen for long, all sites should provide either a way to change the theme or use these CSS features.
[0] https://developer.mozilla.org/en-US/docs/Web/CSS/@media/pref...
[1] https://developer.mozilla.org/en-US/docs/Web/CSS/color-schem...