Microsoft To Do supports dark mode on Windows 10, Android, iOS 13, and macOS Mojave 10.14.2 or later.
To turn on dark mode in Windows 10, head to your Microsoft To Do settings and select Dark theme. You can also select Use my Windows theme.
Microsoft To Do will automatically use your Android theme settings. If you'd like To Do to use a different theme, open your To Do settings and select Theme. You can select from Use my System theme, Light theme, or Dark theme.
Microsoft To Do will automatically use your iOS appearance settings. To turn on dark mode, navigate to your device's Settings > Display & Brightness. Under Appearance, select Dark.
Microsoft To Do will automatically use your Mac appearance settings. Navigate to System Preferences > General. Under Appearance, select Dark.