JSFiddle - React, Tailwind, and code Playground

HTML

<div class="top"></div>
<div class="bottom"></div>

CSS

.top {
  height: 50px;
  width: 100vw;
  background: red;
}
.bottom {
  height: calc(100vh - 50px);
  width: 100vw;
  background: blue;
}