JSFiddle - React, Tailwind, and code Playground

HTML

<div id="rolagem"><div id="rolagem2"></div></div>

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CSS

body, html {
color: #000000;
margin: 0;
height: 5000px;
overflow-y: hidden;
}

.unselectable {
   -moz-user-select: none;
   -khtml-user-select: none;
   -webkit-user-select: none;
   -ms-user-select: none;
   user-select: none;
}

#rolagemsetacima {
float: left;
border-left: 5px solid transparent;
border-right: 5px solid transparent;
border-bottom: 5px solid #F4F4F4;
margin-top: 3px;
}


#rolagemsetabaixo {
float: left;
border-left: 5px solid transparent;
border-right: 5px solid transparent;
border-top: 5px solid #F4F4F4;
margin-top: 3px;
}

#rolagemcima {
position: fixed;
right:1px;
width: 10px;
height: 12px;
background-color: #FFF;
border: #F4F4F4 solid 2px;
-webkit-box-shadow: 0px 0px 5px 0px rgba(50, 50, 50, 0.75);
-moz-box-shadow:    0px 0px 5px 0px rgba(50, 50, 50, 0.75);
box-shadow:         0px 0px 5px 0px rgba(50, 50, 50, 0.75);
}

#rolagembaixo {
position: fixed;
bottom: 0;
right:1px;
width: 10px;
height: 12px;
background-color: #FFF;
border: #F4F4F4 solid 2px;
-webkit-box-shadow: 0px 0px 5px 0px rgba(50, 50, 50, 0.75);
-moz-box-shadow:    0px 0px 5px 0px rgba(50, 50, 50, 0.75);
box-shadow:         0px 0px 5px 0px rgba(50, 50, 50, 0.75);
}

#rolagem2 {
position: fixed;
right:1px;
width: 10px;
background-color: #FFF;
border: #F4F4F4 solid 2px;
-webkit-box-shadow: 0px 0px 5px 0px rgba(50, 50, 50, 0.75);
-moz-box-shadow:    0px 0px 5px 0px rgba(50, 50, 50, 0.75);
box-shadow:         0px 0px 5px 0px rgba(50, 50, 50, 0.75);
}


#rolagem {
position: fixed;
top: 0px;
right:0px;
width: 12px;
height: 100%;
background-color: #FFF;
border: #F4F4F4 solid 2px;
-webkit-box-shadow: 0px 0px 3px 0px rgba(50, 50, 50, 0.75);
-moz-box-shadow:    0px 0px 3px 0px rgba(50, 50, 50, 0.75);
box-shadow:         0px 0px 3px 0px rgba(50, 50, 50, 0.75);
}

JavaScript

var margem = 0;
function criarBarraDeRolagem(){
if ($( document ).height() < $( window ).height()) 
{
return; 
}
var tamanho = $( window ).height() / $( document ).height();
$('#rolagem2').css('top', margem + ($( window ).scrollTop() * tamanho));
$('#rolagem2').height($( window ).height() * tamanho - (margem + margem) );
}

$(document).ready(function(){
criarBarraDeRolagem();
});



var dragObj = null;
$("#rolagem2, body, html").mouseup(function(){
$('body, html').removeClass("unselectable");
dragObj = null;
});

$("#rolagem2").mousedown(function(){
$('body, html').addClass("unselectable");
dragObj = this;
});

$("#rolagem2, body, html").mousemove(function(e){
if( dragObj ) 
{
var move = e.pageY - $("#rolagem").offset().top;
$(window).scrollTop(move * 11.5); // O PROBLEMA ESTÁ AQUI
criarBarraDeRolagem();
e.stopPropagation();
e.preventDefault();
}	
});