As a lot of phones have AMOLED display whenever a desired notification comes the app brings in a black screen with edge lighting.

To use it:
1. Disable any battery optimisation for the app.
2. Give notification access permission.
3 Select apps you want notifications for, by choosing a color
Thats it.

For MIUI 11 devices make sure that AutoStart is enabled in App Info. Also check "Show on lock screen" permission in other settings.
Settings image: https://drive.google.com/folderview?id=1yxrLd5u7kLSGBwviKhXYqM21YLC8Dhiv

Additional Features:
1. Change blink animation time.
2. Change edge colours.
3. Notify for missed calls.
4. Change edge radius to fit various screens
5. Add Downtime