JSFiddle - React, Tailwind, and code Playground

HTML

<div class="absolute"></div>

<div class="line"></div>

CSS

body,
html {
   min-height: 100%;
   position: relative;
   height: 100%;
}

.absolute {
    position: absolute;
    background: gray;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    z-index: -1;
}

.line {
    
    position: relative;
    width: 30%;
    background: blue;
    height: 120%;
}