[HTML Theme]: Add "Navigate to Top" Button

[kavania2002]

Feature

• Feature

Purpose

• Provide a quick and convenient way for users to return to the top of the page
• Eliminate the need for excessive scrolling, especially on long pages
• Improve overall user experience and accessibility

Detail

• Inspired by the navigation feature in the Furo theme
• Implementation:
  • Custom CSS for styling the button
  • Custom JavaScript for button functionality
  • Button positioned at the bottom centre of the page
  • Smooth scrolling animation when the button is clicked
• Current behaviour: Scrolls to the top of the page when clicked

Relates

• Resolves #12558