JSFiddle - React, Tailwind, and code Playground

HTML

<div id="overview">
    <div id="scrollbox">
    </div>
</div>
<div id="main"></div>

CSS

#overview {
    width: 60px;
    height: 1000px;
    float: left;
    border: 1px solid red;
    margin-right: 10px;
    position: fixed;
}

#scrollbox {
    width: 60px;
    height: 60px;
    margin-top: 10px;
    background: black;
}

#main {
    width: 200px;
    height: 1000px;
    border: 1px solid blue;
    float: left;
    margin-left: 70px;
}

JavaScript

/*!
 * jQuery UI 1.8.11
 *
 * Copyright 2011, AUTHORS.txt (http://jqueryui.com/about)
 * Dual licensed under the MIT or GPL Version 2 licenses.
 * http://jquery.org/license
 *
 * http://docs.jquery.com/UI
 */
(function(c,j){function k(a){return!c(a).parents().andSelf().filter(function(){return c.curCSS(this,"visibility")==="hidden"||c.expr.filters.hidden(this)}).length}c.ui=c.ui||{};if(!c.ui.version){c.extend(c.ui,{version:"1.8.11",keyCode:{ALT:18,BACKSPACE:8,CAPS_LOCK:20,COMMA:188,COMMAND:91,COMMAND_LEFT:91,COMMAND_RIGHT:93,CONTROL:17,DELETE:46,DOWN:40,END:35,ENTER:13,ESCAPE:27,HOME:36,INSERT:45,LEFT:37,MENU:93,NUMPAD_ADD:107,NUMPAD_DECIMAL:110,NUMPAD_DIVIDE:111,NUMPAD_ENTER:108,NUMPAD_MULTIPLY:106,
NUMPAD_SUBTRACT:109,PAGE_DOWN:34,PAGE_UP:33,PERIOD:190,RIGHT:39,SHIFT:16,SPACE:32,TAB:9,UP:38,WINDOWS:91}});c.fn.extend({_focus:c.fn.focus,focus:function(a,b){return typeof a==="number"?this.each(function(){var d=this;setTimeout(function(){c(d).focus();b&&b.call(d)},a)}):this._focus.apply(this,arguments)},scrollParent:function(){var a;a=c.browser.msie&&/(static|relative)/.test(this.css("position"))||/absolute/.test(this.css("position"))?this.parents().filter(function(){return/(relative|absolute|fixed)/.test(c.curCSS(this,
"position",1))&&/(auto|scroll)/.test(c.curCSS(this,"overflow",1)+c.curCSS(this,"overflow-y",1)+c.curCSS(this,"overflow-x",1))}).eq(0):this.parents().filter(function(){return/(auto|scroll)/.test(c.curCSS(this,"overflow",1)+c.curCSS(this,"overflow-y",1)+c.curCSS(this,"overflow-x",1))}).eq(0);return/fixed/.test(this.css("position"))||!a.length?c(document):a},zIndex:function(a){if(a!==j)return this.css("zIndex",a);if(this.length){a=c(this[0]);for(var b;a.length&&a[0]!==document;){b=a.css("position");
if(b==="absolute"||b==="relative"||b==="fixed"){b=parseInt(a.css("zIndex"),10);if(!isNaN(b)&&b!==0)return b}a=a.parent()}}return 0},disableSelection:function(){return...