JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  <div id="a"></div>
  <div id="b"></div>
</div>
<div>
  <div id="c"></div>
  <div id="d"></div>
</div>

CSS

body > div {
  height: 50px;
  /* display: flex; */
  font-size: 0; /* remove inline block whitespace */
}
body > div > div {
  /* flex: 1; */
  box-sizing: border-box;
  height: 50px;
  display: inline-block;
  width: 50%;
}
#a {
  background-color: red;
}
#b {
  background-color: green;
}
#c {
  padding: 10px;
  background-color: blue;
}
#d {
  background-color: yellow;