Themes & accent color

  1. Open Settings — the General tab covers appearance.
  2. Turn on Follow system theme to match your device, or turn it off and set Dark mode manually.
  3. Use the Background darkness slider to fine-tune how black the background is in dark mode.
Settings → General, showing Follow system theme, Dark mode, and the Background darkness slider

You can also pick a custom accent color, with a different color available per library.