JSFiddle - React, Tailwind, and code Playground

HTML

<div class="box">
<div class="rela">
LEFT = 0
</div>
<div class="relb">
LEFT = 100px
</div>
</div>

CSS

.box {
  position: relative;
  height: 200px;
  width: 200px;
  border: 1px red solid;
  
}

.rela {
  position: relative;
  height: 100px;
  width: 100px;
  border: 1px green solid;
  left: 0;  
}
.relb {
  position: relative;
  height: 100px;
  width: 100px;
  border: 1px blue solid;
  left: 100px;
}