fix the nav bar

[saras-69]

Description

This pull request implements a fixed navbar that remains at the top of the page when users scroll, ensuring that navigation links are always accessible. This change improves user experience by allowing easier and more seamless navigation.

Fixes #1603

Type of change

• [ ] Added a new machine learning frameworks, libraries or software.
• [ ] Documentation update

Checklist:

• [ X] My code follows the style guidelines of this project
• [ X] I have performed a self-review of my own code
• [X] I have commented my code, particularly in hard-to-understand areas
• [ X] I have made corresponding changes to the documentation
• [X ] My changes generate no new warnings

[github-actions[bot]]

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