JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="rect">The width must be as long as underlying boxes.</div>
    <div class="box">BOX</div>
    <div class="box">BOX</div>
    <div class="box">BOX</div>
    <div class="box">BOX</div>
    <div class="box">BOX</div>
    <div class="box">BOX</div>
    <div class="box">BOX</div>
    <div class="box">BOX</div>
    <div class="box">BOX</div>
</div>

CSS

*
{
    margin: 2px;
}

.container
{
    width: 100%;
    border: 1px solid black;
}

.box
{
    display: inline-block;
    width:100px;
    height:100px;
    border: 1px solid red;
}

.rect
{
    border: 1px solid green;
}