To ensure a GUI behaves consistently across different operating systems:

1. Use cross-platform GUI frameworks or libraries (e.g., Qt, wxWidgets, Flutter).

2. Follow platform-independent design principles.

3. Avoid OS-specific APIs or use abstraction layers.

4. Test on multiple platforms and devices.

5. Use virtual machines or emulators for testing.

6. Consider using a consistent UI toolkit or theme.

7. Handle platform-specific quirks and bugs.

8. Use continuous integration and testing.

9. Monitor user feedback and reports.

10. Regularly update and refine the GUI.

Additionally:

1. Use standardized UI components and controls.

2. Avoid hardcoded values or assumptions.

3. Use relative positioning and sizing.

4. Test with different fonts, languages, and locales.

5. Consider using a GUI abstraction layer or wrapper.

By following these guidelines, you can ensure a consistent GUI experience across various operating systems, devices, and platforms.