Position in Bootstrap 4?

Question

css

A div with the upline class was able to be displayed on top of the parent only by setting the general css style, and even absolute, because relative does not pop up. Isn't there a built-in method in Bootstrap 4?

<div class="container-fluid">
     <div class="row dual">
          <div class="col"></div>
          <div class="col">
               <div class="row upline"></div>
          </div>
     </div>
</div>

upline {
  z-index: 1000;
  position: absolute;
  background-color: green
}