JSFiddle - React, Tailwind, and code Playground

HTML

<div class="box">
  <div>
    <span>This is a relatively sticky header</span>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Delectus voluptas pariatur ullam, dolores veritatis vero possimus nisi corrupti, provident aspernatur harum ab aliquam expedita assumenda, blanditiis aliquid id consequuntur distinctio.</p>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Delectus voluptas pariatur ullam, dolores veritatis vero possimus nisi corrupti, provident aspernatur harum ab aliquam expedita assumenda, blanditiis aliquid id consequuntur distinctio.</p>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Delectus voluptas pariatur ullam, dolores veritatis vero possimus nisi corrupti, provident aspernatur harum ab aliquam expedita assumenda, blanditiis aliquid id consequuntur distinctio.</p>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Delectus voluptas pariatur ullam, dolores veritatis vero possimus nisi corrupti, provident aspernatur harum ab aliquam expedita assumenda, blanditiis aliquid id consequuntur distinctio.</p>
  </div>
</div>

CSS

.box {
  height: 300px;
  background-color: #ddd;
  overflow: auto;
  margin-top: 70px;
}

div > div {
  height: 1000px;
  position: relative;
}

span {
  display: block;
  height: 20px;
  background-color: tomato;
  position: sticky;
  top: 0;
}