JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://code.jquery.com/ui/1.9.2/themes/base/jquery-ui.css">
<ol id="selectable">
  <li class="ui-state-default">1</li>
  <li class="ui-state-default">2</li>
  <li class="ui-state-default">3</li>
  <li class="ui-state-default">4</li>
</ol>

CSS

#feedback { font-size: 1.4em; }
  #selectable .ui-selecting { background: #FECA40; }
  #selectable .ui-selected { background: #F39814; color: white; }
  #selectable { list-style-type: none; margin: 0; padding: 0; width: 250px; }
  #selectable li { margin: 3px; padding: 1px; width: 100px; height: 100px; font-size: 4em; text-align: center; }

JavaScript

$(function() {
    var _mousedown = false;
    $('#selectable').selectable({
        start: function(event,ui){
            _mousedown=true;
        },
        stop: function(event,ui){
            _mousedown=false;
            $('.ui-selected').removeClass('ui-selected');
            $('.selecting').addClass('ui-selected');
        },
        selecting: function(event,ui){
            if($('.ui-selecting').length == 1)
                $(ui.selecting).addClass('selecting');
            
            $('.ui-selecting').removeClass('ui-selecting');
            $('.selecting').addClass('ui-selecting');
        },
        unselecting: function(event,ui){
            if($(ui.unselecting).hasClass('selecting'))
                $(ui.unselecting).removeClass('selecting');
        }
    });
    
    $('#selectable').on('mouseenter', '.ui-selectee', function(){
        if(_mousedown)
            $(this).addClass('selecting');
    });
  });