Implemented the sticky behavior for the light mode and dark mode buttons

[namrata18s]

Fixes Issue

Addresses the issue by implementing sticky behavior for the Light Mode and Dark Mode buttons, ensuring they remain visible and accessible as the user scrolls. This enhancement improves the user experience and provides easy access to theme switching.

Closes #394

Changes proposed

Check List (Check all the applicable boxes)

• [x ] My code follows the code style of this project.
• My change requires changes to the documentation.
• I have updated the documentation accordingly.
• [x ] All new and existing tests passed.
• [X ] This PR does not contain plagiarized content.
• [X ] The title of my pull request is a short description of the requested changes.

Screenshots

Note to reviewers