Improve scroll-to-top button styling and behavior

[ankitkr104]

Summary

This PR improves the scroll-to-top button so it is cleaner, more accessible, and visually aligned with the site's white/gray theme.

Changes made

• Replaced text-based button content with an inline SVG arrow icon.
• Converted the button shape from rectangular to circular.
• Updated button styling to a white/gray theme:
  • white background
  • subtle gray border
  • gray icon color
  • subtle shadow
• Reduced button size for a less intrusive footprint.
• Increased arrow height to improve visibility.
• Improved hover state styling for clearer affordance.
• Updated scroll behavior JS so the button displays using flex (keeps icon centered consistently).

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[Copilot]

Pull request overview

This PR updates the “scroll to top” button to better match the site’s white/gray theme and improve its UI consistency by switching to an icon-based, circular button and aligning the JS behavior with the new layout needs.

Changes:

• Updated the scroll-to-top button markup to use an inline SVG arrow icon with improved accessible labeling.
• Refreshed button styling (circular shape, white/gray palette, hover affordance, centered icon).
• Adjusted scroll handler to show the button using display: flex for consistent centering.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
assets/js/button.js	Shows/hides the button on scroll, updated to use display: flex when visible.
assets/css/button.scss	Restyles the button to a circular white/gray design and sizes the SVG icon.
_includes/footer.html	Replaces text label with an inline SVG icon and adds aria-label.

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