JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://code.jquery.com/ui/1.10.3/themes/smoothness/jquery-ui.css">
<div class="scroll-pane ui-widget ui-widget-header ui-corner-all">
  <div class="scroll-content">
    <div class="scroll-content-item ui-widget-header">1</div>
    <div class="scroll-content-item ui-widget-header">2</div>
    <div class="scroll-content-item ui-widget-header">3</div>
    <div class="scroll-content-item ui-widget-header">4</div>

  </div>
  <div class="scroll-bar-wrap ui-widget-content ui-corner-bottom">
    <div class="scroll-bar"></div>
  </div>
</div>
 

<input type='button' value='Add New Block' class='addNew'/>

CSS

.scroll-pane { overflow: auto; width: 99%; float:left; }
  .scroll-content { width: 2440px; float: left; }
  .scroll-content-item { width: 100px; height: 100px; float: left; margin: 10px; font-size: 3em; line-height: 96px; text-align: center; }
  .scroll-bar-wrap { clear: left; padding: 0 4px 0 2px; margin: 0 -1px -1px -1px; }
  .scroll-bar-wrap .ui-slider { background: none; border:0; height: 2em; margin: 0 auto;  }
  .scroll-bar-wrap .ui-handle-helper-parent { position: relative; width: 100%; height: 100%; margin: 0 auto; }
  .scroll-bar-wrap .ui-slider-handle { top:.2em; height: 1.5em; }
  .scroll-bar-wrap .ui-slider-handle .ui-icon { margin: -8px auto 0; position: relative; top: 50%; }

JavaScript

$(function() {
    //scrollpane parts
    var scrollPane = $( ".scroll-pane" ),
      scrollContent = $( ".scroll-content" );
 
    //build slider
    var scrollbar = $( ".scroll-bar" ).slider({
      slide: function( event, ui ) {
        if ( scrollContent.width() > scrollPane.width() ) {
          scrollContent.css( "margin-left", Math.round(
            ui.value / 100 * ( scrollPane.width() - scrollContent.width() )
          ) + "px" );
        } else {
          scrollContent.css( "margin-left", 0 );
        }
      }
    });
 
    //append icon to handle
    var handleHelper = scrollbar.find( ".ui-slider-handle" )
    .mousedown(function() {
      scrollbar.width( handleHelper.width() );
    })
    .mouseup(function() {
      scrollbar.width( "100%" );
    })
    .append( "<span class='ui-icon ui-icon-grip-dotted-vertical'></span>" )
    .wrap( "<div class='ui-handle-helper-parent'></div>" ).parent();
 
    //change overflow to hidden now that slider handles the scrolling
    scrollPane.css( "overflow", "hidden" );
 
    //size scrollbar and handle proportionally to scroll distance
    function sizeScrollbar() {
      var remainder = scrollContent.width() - scrollPane.width();
      var proportion = remainder / scrollContent.width();
      var handleSize = scrollPane.width() - ( proportion * scrollPane.width() );
      scrollbar.find( ".ui-slider-handle" ).css({
        width: handleSize,
        "margin-left": -handleSize / 2
      });
      handleHelper.width( "" ).width( scrollbar.width() - handleSize );
    }
 
    //reset slider value based on scroll content position
    function resetValue() {
      var remainder = scrollPane.width() - scrollContent.width();
      var leftVal = scrollContent.css( "margin-left" ) === "auto" ? 0 :
        parseInt( scrollContent.css( "margin-left" ) );
      var percentage = Math.round( leftVal / remainder * 100 );
      scrollbar.slider( "value", percentage );
    }
 
    //if the slider is 100% and window gets...