JSFiddle - React, Tailwind, and code Playground

HTML

<html>
    <head>
    </head>
    <body>
        <div id="div1" style="position: fixed; left: 0; width: 100%; height: 95%; border: 1px red solid; overflow: auto">
            Lorem ipsum<br/>
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            Lorem ipsum<br/>
            Lorem ipsum<br/>
            Lorem ipsum<br/>
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       ...

JavaScript

var d1 = document.getElementById('div1'),
    d2 = document.getElementById('div2');

function s() {
 
 var p = (d1.scrollHeight - d1.clientHeight) / d1.scrollTop,
     x = (d2.scrollHeight - d2.clientHeight) / p;
 
 d2.scrollTop = Math.round(x);
    
}

d1.onscroll = s;