JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <div class="parent-wrapper">
        <div class="parent">
            <div class="child">1</div>
            <div class="child">2</div>
            <div class="child">3</div>
            <div class="child">4</div>
            <div class="child">5</div>
            <div class="child">6</div>
            <div class="child">7</div>
        </div>
    </div>
</body>

CSS

.parent-wrapper {
    height:100%;
    width: 400px;
    border: 1px solid black;
}
.parent {
    display: flex;
    flex-wrap:wrap;
}
.child {
    background:blue;
    flex: 1 0 21%;
    height:100px;
    margin: 5px;
}