JSFiddle - React, Tailwind, and code Playground

HTML

<div class="flexbox">
    <div class="box box1">child 1</div>
    <div class="box box2">child 2</div>
    <div class="box box3">child 3</div>
    <!--div class="box box4">child 4</div-->
</div>

CSS

.flexbox {
    background-color: yellow;
    display: -webkit-flex;
    -webkit-box-orient: horizontal;
    display: -moz-box;
    -moz-box-orient: horizontal;
    display: box;
    -webkit-flex-direction: row;
    -webkit-flex-wrap: wrap;
    box-orient: horizontal;
    width: 100%;
    height: 300px;
}
.box {
    -moz-box-flex: 1;
    width: 50%;
    height: 100px;
}
.box1 {
    background-color: lime;
}
.box2 {
    background-color: blue;
}
.box3 {
    background-color: red;
}
.box4 {
    background-color: green;
}