A setup is a mode plus brightness, contrast and colour tweaks. Make one for each purpose (day, night, reading) and switch in the toolbar popup. Changes save automatically. Each site can also be forced dark, light or off from the popup.
Mode
Make pagesDark makes light pages dark. Light makes dark pages light. System follows your computer's theme. Schedule is dark between two times. A page that already matches is left alone.
ScheduleDark from the first time until the second (it can run past midnight).
to
Look
Brightness
Contrast
Sepia (warm tint)Easier on the eyes in the evening.
Grayscale
Keep photos and videos naturalImages, video, canvas, embedded frames and CSS background photos keep their real colours. Turn off to invert everything (logos that are dark on transparent show up better).
Sites with their own choice
Set from the toolbar popup or with Alt+Shift+D (switches the current site between dark and light). Change the shortcut at chrome://extensions/shortcuts (brave://, edge://).