feat(UI) : update homepage, navbar, and quiz container styling with new gradients and shadows.

[DivyanshiSingh-23]

📌 What does this PR do?

This PR refreshes the quiz app UI by applying new gradient backgrounds and matching shadows to key elements for a cleaner and more modern look.

🔧 Type of Change

• Bug fix (non-breaking change)
• New feature
• Breaking change
• Documentation update

✅ How Has This Been Tested?

Manually verified gradient backgrounds and shadows correctly in chrome.
Checked color contrast to ensure text remains readable.

📊 Impact / Performance

Improves user readability and visual consistency across the UI.

✅ Checklist

• I have followed the code style guidelines.
• I have self-reviewed my code.
• I have commented on complex parts of the code.
• I have updated or added documentation where necessary.
• All tests pass locally.
• No new warnings have been introduced.