JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <div class="flex-container">
        <div class="flex-item">1</div>
        <div class="flex-item">2</div>
        <div class="flex-item">3</div>
        <div class="flex-item">4</div>
        <div class="flex-item">5</div>
        <div class="flex-item">6</div>
        <div class="flex-item">7</div>

        <div class="flex-item">1</div>
        <div class="flex-item">2</div>
        <div class="flex-item">3</div>
        <div class="flex-item">4</div>
        <div class="flex-item">5</div>
        <div class="flex-item">6</div>
        <div class="flex-item">7</div>
        <div class="flex-item">1</div>
        <div class="flex-item">2</div>
        <div class="flex-item">3</div>
        <div class="flex-item">4</div>
        <div class="flex-item">5</div>
        <div class="flex-item">6</div>
        <div class="flex-item">7</div>
    </div>
</body>

CSS

.flex-container {
    padding: 0;
    margin: 0;
    list-style: none;
    display: flex;
    flex-wrap: wrap;
    align-content: flex-start;
}
.flex-item {
    background: tomato;
    margin: 5px;
    color: white;
    font-weight: bold;
    font-size: 1.5rem;
    text-align: center;
    flex: 0 0 3rem;
    height:auto;
    display: flex;
}
.flex-item:before {
    content:'';
    display:inline-block;
    vertical-align:middle;
    padding-top:100%;

}