JSFiddle - React, Tailwind, and code Playground

by hcarleton

HTML

<div class="parent">
    <div class="box"></div>
</div>
<div class="tall"></div>

CSS

body { margin: 0; }
html {
    box-sizing: border-box;
}
*, *::before, *::after {
    box-sizing: inherit;
    position: relative;
}
.parent {
    position: static; /* .box will get it's percentage width form the body element */
    background: rgba(0, 0, 0, .4);
    height: 100px;
    width: 5rem;
    margin-bottom: 25px;
}

.box {
    position: absolute;
    top: 0;
    left: 0;
    height: 50px;
    width: 100%; /* 100% of body width */
    background: rgba(0, 0, 0, .4);
    border: 2px solid red;
}

.tall {
    height: 100rem;
}