Tampermonkey script, make auto scroll with js

I want to make a tampermonkey script but I have zero knowledge. Purpose to read comic easier without scrolling.

I want to make tampermonkey with button on the page, location: right, down side. When i click the button it will auto scroll from up to down. And also if you can add speed variant like a volume of youtube: drag up(slower), drag down(faster).

I have an example of the auto scroll, links: https://codepen.io/michaelvinci/pen/qKVBLG?page=1&

Here's the button look like on the web: Button on web

here is code source From https://codepen.io/michaelvinci/pen/qKVBLG?page=1&:

<script src='https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js'></script><script  src="./script.js"></script>

and script.js

let x = 0;
let startScroll;

$('.scrollable').scroll(function () {
  x = $(this).scrollTop();
})

$('#scroll-slider').on('input', function () {
  clearInterval(startScroll);
 
  
  if ($('#pause').hasClass('active')) {
    startScroll = setInterval(scroller, 400 / ($('#scroll-slider').val())); 
  }
});

$('.scroll-btn').on('click', function () {
  $('#play').toggleClass('active');
  $('#pause').toggleClass('active');
  
  if ($('#pause').hasClass('active')) {
    startScroll = setInterval(scroller, 800 /($('#scroll-slider').val()) ); 
  } else {
    clearInterval(startScroll);
  }
});

function scroller () {
  x += 1
  $('.scrollable').scrollTop(x); 
}