JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
<div class="block">

</div>
<div class="absolute">

</div>
</div>

CSS

.container {
  display: flex;
  justify-content: flex-end;
  position: relative;
  width: 400px;
  height: 300px;
}

.block {
  border: 1px solid blue;
     width: 40px;
  height: 300px;
}

.absolute {
  border: 1px solid red;
  position: absolute;
  top: 0;
  left: 0;
   width: 400px;
  height: 40px;
  background: yellow;
}