There is a known bug in Chromium where it can't detect the preferred theme of the system OS, so it always sets it as default (light theme).
An often given "solution" is enable the Chrome flag #enable-force-dark, but it doesn't really solve the problem, the CSS "prefer-color-scheme" media query is always set to light, no matter what you do.
One temporary solution that I think is to force the "prefer-color-scheme" query globally on Chrome. I know that you can force it in the Dev tools at F12 Three dots > More tools > Rendering > Emulate CSS media feature prefers-color-scheme, but it will only be active in the current page context for Developing purposes, so, How can I set the prefer-color-scheme to dark globally?, maybe with a Chrome extension?
A workaround:
Launch Chrome/Chromium with the --force-dark-mode flag (aka command line switch).
google-chrome --force-dark-mode
Put this flag in /usr/share/applications/google-chrome.desktop file, specifically in the Exec key. Preferably add it to ~/.local/share/applications/google-chrome.desktop since user entries take precedence over system entries, and this key wont be overwritten by Chrome updates.