JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <div class="header"></div>
    <div class="categories"></div>
    <div class="content"></div>
</body>

CSS

html, body {
  height: 100%;
}
body{
    margin:0;
    padding:0;
}

.header{
    padding-top:0;
    margin-top:0;
    height:160px;
    background:#666;
}

.categories{
    position: absolute;
    height: calc(100% - 160px);
    width:20%;
    background:#b6fd40;
}

.content{
  height: calc(100% - 160px);
  background: gray;
}