JSFiddle - React, Tailwind, and code Playground

HTML

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

<div class="parent2">
    <div class="box"></div>
</div>

CSS

.parent {
    background: rgba(0, 0, 0, .4);
    height: 100px;
    width: 100%;
    margin-bottom: 25px;
}

.box {
    background: rgba(0, 0, 0, .4);
    height: 50px;
    width: 100wv;
}

.parent2 {
    background: rgba(0, 0, 0, .4);
    height: 100px;
    width: 100%;
    padding: 10px;
}