JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="box box1"></div>
    <div class="box box2"></div>
</div>

CSS

.container {
    display: flex;
}

.box {
    flex: 1;
    height: 50px;
    border: 1px solid #aaa;
}

.box1 {
    /* display: none; */
    background-color: aqua;
}

.box2 {
    /* display: none; */
    background-color: red;
}