JSFiddle - React, Tailwind, and code Playground

HTML

<div class="flex">
    <div class="item">A</div>
    <div class="item">B</div>
</div>

CSS

.flex {
    background: green;
    display: flex;
}

.flex .item:first-child {
    background: red;
    width: 200px;
}

.flex .item:last-child {
    background: yellow;
    width: 200px;
}