Improve “scroll to” button

[xplosionmind]

• [x] a vanilla JavaScript main version
  • [x] create the HTML with JS
  • [ ] Add sound effect (Elevator.js?) (#58)
  • [x] optimize the current code: the button should be turned when the page is open, not only at first scroll.
• [x] a noscript alternate version

Resources

• https://www.w3schools.com/howto/howto_js_scroll_to_top.asp
• https://stackoverflow.com/questions/67610648/how-can-%C4%B1-make-scroll-button
• https://w3collective.com/responsive-step-progress-bar
• https://css-tricks.com/need-to-scroll-to-the-top-of-the-page