Hi there! I see that your Blue Mountain Ecards app is opening to just a black screen on your Mac running OS X 10.15.7. Let’s get this sorted out for you.

First, I want to understand a bit more:
- When did this issue start happening?
- Have you tried restarting your Mac or the app already?
- Is this the native Blue Mountain Ecards app or are you accessing Blue Mountain Ecards via a browser?

Meanwhile, here are some simple steps you can try that often resolve black screen issues on apps:

1. Force Quit and Reopen the App
- Click on the Apple menu () top-left → select "Force Quit"
- Choose the Blue Mountain Ecards app and click "Force Quit"
- Then reopen the app and see if it loads properly

2. Restart Your Mac
- Sometimes a fresh start clears up temporary glitches. Just click Apple menu → Restart.

3. Check for App Updates
- Open the App Store on your Mac → Go to Updates → If Blue Mountain Ecards app update is available, install it.

4. Clear App Cache or Saved Data
On Mac apps, this can vary, but if there’s a way in your app's settings to clear cache/data, try that. Otherwise, uninstall and reinstall the app (I can guide you through this).

5. Check for macOS Updates
- Go to System Preferences → Software Update → Install any available updates. Older OS versions may sometimes conflict with newer app versions.

If you have already tried these or the problem continues, we can look into deeper troubleshooting such as checking app permissions, graphics settings, or possible compatibility issues with OS X 10.15.7.

Could you please let me know what you’ve tried so far? That way, I can tailor the next steps perfectly for your situation.