JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<button type="submit" id="button" style="display: none; height: 30px; position: absolute; z-index: 2;">Применить</button>
<div id = 'checks-block' style = 'border: 1px solid black; z-index: 1;'>
  <div style="display: block;">
    <div tabindex="0" style="overflow: hidden; padding: 0px; width: 193px; border: 1px solid orange;">     
      <div style="width: 193px; height: 500px;">
        <div style="padding: 0px; left: 0px; top: 0px; width: 180px;">
          <ul class="check-list">
            <li>
              <input type="checkbox" id="1" checked="" value="13794">
              <label for="1">BARS SILVER</label>
            </li>
            <li>
              <input type="checkbox" id="2" value="13647">
              <label for="2">BLAK HORSE</label>
            </li>
            <li>
              <input type="checkbox" id="3" checked="" value="13659">
              <label for="3">BOSCH</label>
            </li>
            <li>
              <input type="checkbox" id="4" value="13721">
              <label for="4">Brand</label>
            </li>
            <li>
              <input type="checkbox" id="5" value="13835">
              <label for="5">CHAMPION</label>
            </li>
          </ul>
        </div>
      </div>
    </div>
  </div>
</div>

JavaScript

(function ($)
{
	$(document).ready(function () {
		$('.check-list  :checkbox').on('change', function(e) {
		
			// определить последний выбранный элемент
			var lastElement = undefined;
			$(".check-list input[type='checkbox']:checked").each(function(index, element){
				lastElement = element;
			});
			
			if (lastElement == undefined)
				$('#button').hide(300);
			else
			{
        var buttonX = $('#checks-block').offset().left + 200;
        var buttonY = $(lastElement).next().offset().top + ($(lastElement).next().height() - 30 /*высота кнопки*/) / 2;
        
				$('#button').hide(300, function(){
					$('#button').css({left: buttonX, top: buttonY,}).show(300);
				});
			}
		});
	});

}(jQuery));