JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="child">
  </div>
  <div class="child-2">
  </div>
</div>

CSS

.container {
  width: 300px;
  height: 300px;
  border: solid 1px blue;
  position: relative;
}

.child {
  position: absolute;
  width: 50px;
  height: 50px;
  background-color: red;
  position: absolute;
  right: 50%;
  left: 50%;
  top: 50%;
  border-radius: 100%;
}

.child-2 {
  border-bottom: solid 1px blue;
  width: 300px;
  height: 150px;
}