JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="box box1"><span>1</span></div>
    <div class="box box2"><span>2</span></div>
    <div class="box box3"><span>3</span></div>
</div>

CSS

* {
    box-sizing: border-box;
}

.container {
    display: flex;
    flex-direction: column;
    padding: 5px 0;
    background-color: #f5f5f5;
    border: 1px solid #aaa;
}

.box1 { background-color: red; }
.box2 { background-color: lightgreen; }
.box3 { background-color: yellow; }

.box {
    height: 100px;
    width: calc(100% - 20px);
    margin: 5px 10px;
    border: 1px solid #ccc;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.2em;
}

@media (min-width: 800px) {
    .container {
        flex-direction: row;
        flex-wrap: wrap;
    }
    .box {
        flex-basis: 45%;
    }
}