JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outside">
  <div class="inside-1"></div>
  <div class="inside-2"></div>
</div>

CSS

.outside {height:200px; border:1px solid red; position:relative;} 
.inside-1 { 
    height: 10px; 
    width: 20px; 
    border: 1px solid black; 
    position:absolute;
    bottom:0;
    left:50%;
    margin-left: -20px;
}


.inside-2 {
    height: 10px; 
    width: 20px; 
    border: 1px solid black; 
    position:absolute;
    bottom:0;
    left:50%;
    margin-left: 0px;
}