JSFiddle - React, Tailwind, and code Playground

HTML

<div class="flex">
    <div class="flex-item">One</div>
    <div class="flex-item">Two</div>
    <div class="flex-item">Three</div>
    <div class="flex-item">Four</div>
</div>

CSS

.flex {
    display: flex;
}

.flex-item {
    color: white;
    background-color: orange;
    padding: 10px;
    margin: 5px;
    border-radius: 5px;
    flex-grow: 1;
    flex-basis: 0;
    /* box-sizing not working */
    box-sizing: border-box;
}

.flex-item:nth-child(2) {
    border: 20px solid green;
}

.flex-item:nth-child(3) {
    padding: 20px;
}