If you're using the app on an iOS device, you can change its color scheme to light or dark mode. You can also configure it to follow the system's settings.
Steps
Open Profile.
Tap Settings (gear).
Go to Preferences (or Look and Feel).
Tap Color Scheme, choose Light, Dark or System, then tap Looks good!.
The app changes straight away, and the 1SE widget follows the same setting. Here's how each one looks:
 |  |
Light | Dark |
To add the widget, see How to Set Up the 1SE Widget.