Make background colors consistent between About and Contact pages

[Sakshigupta1902]

#353

📝 Description

This pr fixes the inconsistent colour across about and contact

Fixes

-Updated ContactUs.css to use consistent CSS variables for background colors

• Made hero section background match About page gradient
• Ensures proper theme consistency across pages

✅ Checklist Before Submitting

• [yes ] I’ve tested the code locally and it works as expected
• [yes ] I’ve added screenshots if applicable
• [yes ] I’ve followed the code style and contribution guidelines

📸 Screenshots (if applicable)

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[github-actions]

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[Sakshigupta1902]

@agamjotsingh18 please check my pr