JSFiddle - React, Tailwind, and code Playground

HTML

<div class="header">test</div>
  <div class="slider"></div>

CSS

body{
  padding: 0px;
}

.header{
  height: 20px;
  background-color: red;
  box-shadow: 0 2px 8px green;
  position: relative;
  z-index: 1000;
}

.slider{
  position: relative;
  z-index: 1;
  height: 300px;
  background-color: grey;
}