Enhancement(UI improvement): Back button on Fitness page added

[Julliet-Mohanta]

🚀 Pull Request Template

📌 Related Issue

Fixes #919

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📝 Description

🔹 What has been changed?

• Changing the css of back button basically its position as previously it was hidden behind navbar layout
• Improving the z-index of button so that it is visible on page

🔹 Why are these changes needed?

Explain the purpose or problem being solved.
Currently user does not have any option to go back to home page if he/she is on BMI page as there is no back option, forcing the user to reload the page.
Reason for changes: Adding a back button on BMI(Fitness) page like History and Trophy pages to enhance user navigation.

🛠️ Type of Change

Please mark the relevant option(s):

• 🐛 Bug Fix
• ✨ New Feature
• [X ] 🎨 UI/UX Improvement
• 📖 Documentation Update
• [X ] ⚡ Performance Improvement
• 🔧 Refactoring
• 💥 Breaking Change

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🧪 Testing

Describe how you tested your changes.

✅ Tests Performed

• [ X] Tested locally
• [X ] Build runs successfully
• [X ] No console errors
• [X ] Responsive design checked
• [X ] Existing functionality verified

🌐 Browsers Tested

• [X ] Chrome
• Firefox
• [X ] Edge
• Safari

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📷 Screenshots / Demo (if applicable)

Please attach screenshots, GIFs, or demo videos for UI-related changes.

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📋 Checklist

Before submitting this PR, please confirm the following:

• [X ] I have read the project's CONTRIBUTING guidelines
• [ X] My code follows the project style guidelines
• [X ] I have performed a self-review of my code
• [X ] I have tested my changes locally
• [ X] I have added/updated documentation where necessary
• [ X] My changes do not introduce new warnings or errors
• [ X] This PR is linked to an existing issue

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💬 Additional Notes

Add any additional context, references, or information for reviewers here.

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