JSFiddle - React, Tailwind, and code Playground

HTML

<header style="background-color: yellow">
  <div class="aaa" style="background-color:red;"></div>
  <div class="bbb" style="background-color:blue;"></div>
  <div class="ccc" style="background-color:green;"></div>
</header>

CSS

body {
  padding: 0;
  margin: 0;
}
header{
  width: 100%;
  height: 120px;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
div {
  height: 30px;
  width: 30px;
}