JSFiddle - React, Tailwind, and code Playground

HTML

<div class="div1">
    <div class="div2">
        <h3 class="sidetext">Post #NUM</h3>
    </div>
    <div class="div3">
       <p>The main content (text) for this div is written here</p>
    </div>
   
</div>

CSS

.div1 {
  margin-left: 10%;
  margin-right: 10%;
}
.div2 {
  align: left;
  width: 50px; float:left;
  background-color: black;
  margin-right:10px
}
.div3{
 // float:left
}
.sidetext {
  color: white;float:left;
  transform: rotate(270deg);
  transform-origin:22px center 0;
}