[Feature] Redesign Game Screens (Start, Pause, Game Over) with Themed Backgrounds & UI Elements

### 🔍 Have You Searched Existing Issues?

- [x] I have searched the existing issues to avoid duplicates

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### 💡 Problem Description

The current game screens—such as **Start**, **Pause**, and **Game Over**—are minimalistic and could be more engaging. Without themed visuals or styled UI elements, users miss out on a more immersive gaming experience.

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### ✅ Proposed Solution

I propose a complete **UI/UX redesign** for these game states:
- 🎮 **Start Screen**: Add animated background, stylish "Start Game" button, and title.
- ⏸️ **Pause Menu**: Introduce a semi-transparent overlay with "Resume" and "Restart" buttons styled consistently.
- ❌ **Game Over Screen**: Display score clearly, use themed background (e.g., pixel art, retro glow), and add "Play Again" and "Exit" options.

Each screen will follow a **cohesive theme** (e.g., neon, retro, or modern minimalist) using CSS transitions, animations, and visual feedback.

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### 🔄 Alternatives Considered

- Only styling text/buttons without changing layout (less immersive).
- Using default alerts (not user-friendly for games).

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### 🖼️ Screenshots or Diagrams (Optional)

Mockups or references can be shared in comments if required.

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### 📘 Additional Context

This enhancement aligns well with other UI improvements in the repo but specifically focuses on **game states**, which are not covered in-depth by other open issues. It aims to elevate the visual feedback and engagement level during gameplay.

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### 🙌 Contributor Checklist

- [x] I have checked for similar feature requests
- [x] I agree to follow this project's Code of Conduct
- [x] I am a GSSOC'25 contributor
- [x] I want to work on this issue