Fixes Issue : Highlight page navigation when within the section below the header, rather than just when header is in view

closes #13

Changes proposed

• store the last element in extra element if that is not show in screen and make that highlight until another element page navigation is not come on screen

Check List (Check all the applicable boxes)

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

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Note to reviewers