fix: Background for Tabbar Icon

[Darsh0307]

GitHub Issue (If applicable): closes https://github.com/unoplatform/Uno.Gallery/issues/1032

PR Type

What kind of change does this PR introduce?

• [x] Bugfix
• Feature
• Code style update (formatting)
• Refactoring (no functional changes, no api changes)
• Build or CI related changes
• Documentation content changes
• Project automation
• Other... Please describe:

What is the current behavior?

Tabbar-For Material Top TabBar sample Page' the tab Icon and text color is not changing for dark theme

What is the new behavior?

The Text and Icon color should change to black color for dark theme or the whole screen should change in black color.

PR Checklist

Please check if your PR fulfills the following requirements:

• [ ] Tested on iOS.
• [ ] Tested on Wasm.
• [ ] Tested on Android.
• [ ] Tested on UWP.
• [ ] Tested in both Light and Dark themes.
• [ ] Associated with an issue (GitHub or internal)

Other information

Internal Issue (If applicable):