JSFiddle - React, Tailwind, and code Playground

HTML

<div class="category-body">We are in the category-body
  <div class="category-header">We are in the category-header</div>
</div>

CSS

html, body {margin:0;}
.category-body {
    margin-left: 17% !important;
    width: 67%;
    background-color: red;
    height: 500px;
}

.category-header {
    position: fixed;
    top: 51px;
    width: inherit;
    background-color: green;
}